<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a03483-6b9b-79e9-b618-fee1beb4612f,g:6ae246fe-0965-4779-b3ed-e023e27c690e-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.pentair.com/role/CondensedConsolidatedStatementsofChangesinEquity" xlink:type="simple" xlink:href="pnr-20260930.xsd#CondensedConsolidatedStatementsofChangesinEquity"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/CondensedConsolidatedStatementsofChangesinEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a03483-6d09-7a25-880f-73b1292a9e0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a03483-6d09-7ed0-868a-3f98dce4a3ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a03483-6d09-7a25-880f-73b1292a9e0e" xlink:to="loc_us-gaap_StatementTable_01a03483-6d09-7ed0-868a-3f98dce4a3ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a03483-6d09-7ae9-9741-e6b8c1936654" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a03483-6d09-7ed0-868a-3f98dce4a3ad" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a03483-6d09-7ae9-9741-e6b8c1936654" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a03483-6d09-7ae9-9741-e6b8c1936654_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a03483-6d09-7ae9-9741-e6b8c1936654" xlink:to="loc_us-gaap_EquityComponentDomain_01a03483-6d09-7ae9-9741-e6b8c1936654_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a03483-6d09-7b41-8194-7af066d196bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a03483-6d09-7ae9-9741-e6b8c1936654" xlink:to="loc_us-gaap_EquityComponentDomain_01a03483-6d09-7b41-8194-7af066d196bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a03483-6d09-7126-b337-5d008de1733c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a03483-6d09-7b41-8194-7af066d196bd" xlink:to="loc_us-gaap_CommonStockMember_01a03483-6d09-7126-b337-5d008de1733c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_01a03483-6d09-7745-9deb-7437374f73c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a03483-6d09-7b41-8194-7af066d196bd" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_01a03483-6d09-7745-9deb-7437374f73c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a03483-6d09-7b65-b81f-95dd5d8bc571" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a03483-6d09-7b41-8194-7af066d196bd" xlink:to="loc_us-gaap_RetainedEarningsMember_01a03483-6d09-7b65-b81f-95dd5d8bc571" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a03483-6d09-73fc-aa2c-f45cd64bf43c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a03483-6d09-7b41-8194-7af066d196bd" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a03483-6d09-73fc-aa2c-f45cd64bf43c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_01a03483-6d09-7cb6-a324-85a9e34a2936" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a03483-6d09-7a25-880f-73b1292a9e0e" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_01a03483-6d09-7cb6-a324-85a9e34a2936" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a03483-6d09-7a25-880f-73b1292a9e0e" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_01a03483-6d09-7046-a389-2a2f00029003" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_SharesOutstanding_01a03483-6d09-7046-a389-2a2f00029003" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a03483-6d09-703d-9cf9-41b37f568636" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a03483-6d09-703d-9cf9-41b37f568636" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_01a03483-6d09-711d-8748-50f11e1ab13d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_ProfitLoss_01a03483-6d09-711d-8748-50f11e1ab13d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a03483-6d09-7171-8ddd-a66e01c3a879" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a03483-6d09-7171-8ddd-a66e01c3a879" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_01a03483-6d09-7059-ac55-537e826ffaf4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_DividendsCommonStock_01a03483-6d09-7059-ac55-537e826ffaf4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a03483-6d09-784e-ac3d-ffcf476fcec0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a03483-6d09-784e-ac3d-ffcf476fcec0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a03483-6d09-7c3c-8737-f8032e7110be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a03483-6d09-7c3c-8737-f8032e7110be" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_01a03483-6d09-71e5-a7e2-1a4b4d2e6e26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_01a03483-6d09-71e5-a7e2-1a4b4d2e6e26" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_StockIssuedDuringPeriodValueStockOptionsExercisedNetOfSharesTendered_01a03483-6d09-730b-89cb-1895b042145e" xlink:href="pnr-20260930.xsd#pnr_StockIssuedDuringPeriodValueStockOptionsExercisedNetOfSharesTendered"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_pnr_StockIssuedDuringPeriodValueStockOptionsExercisedNetOfSharesTendered_01a03483-6d09-730b-89cb-1895b042145e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_01a03483-6d09-7c06-97d1-b15e72768f52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_01a03483-6d09-7c06-97d1-b15e72768f52" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_01a03483-6d09-7c57-80cb-a8620c09d035" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_01a03483-6d09-7c57-80cb-a8620c09d035" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_01a03483-6d09-78f6-815c-fea0a9902fce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_01a03483-6d09-78f6-815c-fea0a9902fce" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SharesSurrenderedByEmployeesShares_01a03483-6d09-75e5-a08d-549cba0e650f" xlink:href="pnr-20260930.xsd#pnr_SharesSurrenderedByEmployeesShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_pnr_SharesSurrenderedByEmployeesShares_01a03483-6d09-75e5-a08d-549cba0e650f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SharesSurrenderedByEmployees_01a03483-6d09-73ee-bf7f-5a38efbf4054" xlink:href="pnr-20260930.xsd#pnr_SharesSurrenderedByEmployees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_pnr_SharesSurrenderedByEmployees_01a03483-6d09-73ee-bf7f-5a38efbf4054" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_01a03483-6d09-7de5-98e7-ff85f551a4ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03483-6d09-7786-8437-3211d65565c3" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_01a03483-6d09-7de5-98e7-ff85f551a4ef" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_01a03483-6d09-7947-a1f6-b94adee4553a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_01a03483-6d09-735d-ba76-ace71aeef186" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/RevenueGeographicNetSalesInformationbySegmentDetails" xlink:type="simple" xlink:href="pnr-20260930.xsd#RevenueGeographicNetSalesInformationbySegmentDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/RevenueGeographicNetSalesInformationbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03483-6d09-7644-8142-81377625b35c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_01a03483-6d09-734a-a126-f65ec4323f25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03483-6d09-7644-8142-81377625b35c" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a03483-6d09-734a-a126-f65ec4323f25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_01a03483-6d09-7262-b6d1-e466b6969104" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a03483-6d09-734a-a126-f65ec4323f25" xlink:to="loc_srt_StatementGeographicalAxis_01a03483-6d09-7262-b6d1-e466b6969104" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_01a03483-6d09-7262-b6d1-e466b6969104_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_01a03483-6d09-7262-b6d1-e466b6969104" xlink:to="loc_srt_SegmentGeographicalDomain_01a03483-6d09-7262-b6d1-e466b6969104_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_01a03483-6d09-7423-b351-5246a28f4077" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_01a03483-6d09-7262-b6d1-e466b6969104" xlink:to="loc_srt_SegmentGeographicalDomain_01a03483-6d09-7423-b351-5246a28f4077" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_01a03483-6d09-751a-a23e-017d362d0c67" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a03483-6d09-7423-b351-5246a28f4077" xlink:to="loc_country_US_01a03483-6d09-751a-a23e-017d362d0c67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WesternEuropeMember_01a03483-6d09-7ffc-84bf-73a84e6d4c54" xlink:href="pnr-20260930.xsd#pnr_WesternEuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a03483-6d09-7423-b351-5246a28f4077" xlink:to="loc_pnr_WesternEuropeMember_01a03483-6d09-7ffc-84bf-73a84e6d4c54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DevelopingCountriesMember_01a03483-6d09-78ff-8137-ec5b0876b023" xlink:href="pnr-20260930.xsd#pnr_DevelopingCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a03483-6d09-7423-b351-5246a28f4077" xlink:to="loc_pnr_DevelopingCountriesMember_01a03483-6d09-78ff-8137-ec5b0876b023" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherDevelopedCountriesMember_01a03483-6d09-714c-b428-8691f2f2c138" xlink:href="pnr-20260930.xsd#pnr_OtherDevelopedCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a03483-6d09-7423-b351-5246a28f4077" xlink:to="loc_pnr_OtherDevelopedCountriesMember_01a03483-6d09-714c-b428-8691f2f2c138" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesByIndustryAxis_01a03483-6d09-7d65-af88-8aea1ee64d10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesByIndustryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a03483-6d09-734a-a126-f65ec4323f25" xlink:to="loc_us-gaap_EquitySecuritiesByIndustryAxis_01a03483-6d09-7d65-af88-8aea1ee64d10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesIndustryMember_01a03483-6d09-7d65-af88-8aea1ee64d10_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesIndustryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquitySecuritiesByIndustryAxis_01a03483-6d09-7d65-af88-8aea1ee64d10" xlink:to="loc_us-gaap_EquitySecuritiesIndustryMember_01a03483-6d09-7d65-af88-8aea1ee64d10_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesIndustryMember_01a03483-6d09-7d46-b435-0c2c27f4a905" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesIndustryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquitySecuritiesByIndustryAxis_01a03483-6d09-7d65-af88-8aea1ee64d10" xlink:to="loc_us-gaap_EquitySecuritiesIndustryMember_01a03483-6d09-7d46-b435-0c2c27f4a905" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ResidentialSectorMember_01a03483-6d09-7043-a5b1-192c31e50344" xlink:href="pnr-20260930.xsd#pnr_ResidentialSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_01a03483-6d09-7d46-b435-0c2c27f4a905" xlink:to="loc_pnr_ResidentialSectorMember_01a03483-6d09-7043-a5b1-192c31e50344" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_CommercialSectorMember_01a03483-6d09-7f83-9747-70b6952bfebe" xlink:href="pnr-20260930.xsd#pnr_CommercialSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_01a03483-6d09-7d46-b435-0c2c27f4a905" xlink:to="loc_pnr_CommercialSectorMember_01a03483-6d09-7f83-9747-70b6952bfebe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_IndustrialSectorMember_01a03483-6d09-728e-915d-0da8e9bb34fd" xlink:href="pnr-20260930.xsd#pnr_IndustrialSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_01a03483-6d09-7d46-b435-0c2c27f4a905" xlink:to="loc_pnr_IndustrialSectorMember_01a03483-6d09-728e-915d-0da8e9bb34fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a03483-6d09-7747-8f1f-04be2a5d564f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03483-6d09-7644-8142-81377625b35c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a03483-6d09-7747-8f1f-04be2a5d564f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/RevenuePerformanceObligationsDetails" xlink:type="simple" xlink:href="pnr-20260930.xsd#RevenuePerformanceObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/RevenuePerformanceObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_01a03483-6d09-70f6-81d3-21b9a35f5af3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_01a03483-6d09-7dd3-bc3d-b0ac68d5c88a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_01a03483-6d09-70f6-81d3-21b9a35f5af3" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_01a03483-6d09-7dd3-bc3d-b0ac68d5c88a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_01a03483-6d09-778c-8ade-3849680b2f04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_01a03483-6d09-7dd3-bc3d-b0ac68d5c88a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_01a03483-6d09-778c-8ade-3849680b2f04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a03483-6d09-742f-9890-9d0c16a0bd86" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_01a03483-6d09-7dd3-bc3d-b0ac68d5c88a" xlink:to="loc_srt_RangeAxis_01a03483-6d09-742f-9890-9d0c16a0bd86" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03483-6d09-742f-9890-9d0c16a0bd86_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a03483-6d09-742f-9890-9d0c16a0bd86" xlink:to="loc_srt_RangeMember_01a03483-6d09-742f-9890-9d0c16a0bd86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03483-6d09-7ae2-8a6e-a55a9108a431" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a03483-6d09-742f-9890-9d0c16a0bd86" xlink:to="loc_srt_RangeMember_01a03483-6d09-7ae2-8a6e-a55a9108a431" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a03483-6d09-7c66-8b57-c929f504f528" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a03483-6d09-7ae2-8a6e-a55a9108a431" xlink:to="loc_srt_MinimumMember_01a03483-6d09-7c66-8b57-c929f504f528" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a03483-6d09-7d72-969e-37018028efb3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a03483-6d09-7ae2-8a6e-a55a9108a431" xlink:to="loc_srt_MaximumMember_01a03483-6d09-7d72-969e-37018028efb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_01a03483-6d09-75a3-8747-302349a8624f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_01a03483-6d09-70f6-81d3-21b9a35f5af3" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_01a03483-6d09-75a3-8747-302349a8624f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_01a03483-6d09-727e-8acd-a6ae49c23e09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_01a03483-6d09-70f6-81d3-21b9a35f5af3" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_01a03483-6d09-727e-8acd-a6ae49c23e09" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/RevenuePerformanceObligationsDetails_1" xlink:type="simple" xlink:href="pnr-20260930.xsd#RevenuePerformanceObligationsDetails_1"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/RevenuePerformanceObligationsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_01a03483-6d09-70f6-81d3-21b9a35f5af3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_01a03483-6d09-7dd3-bc3d-b0ac68d5c88a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_01a03483-6d09-70f6-81d3-21b9a35f5af3" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_01a03483-6d09-7dd3-bc3d-b0ac68d5c88a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a03483-6d09-742f-9890-9d0c16a0bd86" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_01a03483-6d09-7dd3-bc3d-b0ac68d5c88a" xlink:to="loc_srt_RangeAxis_01a03483-6d09-742f-9890-9d0c16a0bd86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03483-6d09-742f-9890-9d0c16a0bd86_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a03483-6d09-742f-9890-9d0c16a0bd86" xlink:to="loc_srt_RangeMember_01a03483-6d09-742f-9890-9d0c16a0bd86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03483-6d09-7ae2-8a6e-a55a9108a431" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a03483-6d09-742f-9890-9d0c16a0bd86" xlink:to="loc_srt_RangeMember_01a03483-6d09-7ae2-8a6e-a55a9108a431" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a03483-6d09-7c66-8b57-c929f504f528" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a03483-6d09-7ae2-8a6e-a55a9108a431" xlink:to="loc_srt_MinimumMember_01a03483-6d09-7c66-8b57-c929f504f528" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a03483-6d09-7d72-969e-37018028efb3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a03483-6d09-7ae2-8a6e-a55a9108a431" xlink:to="loc_srt_MaximumMember_01a03483-6d09-7d72-969e-37018028efb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_01a03483-6d09-75a3-8747-302349a8624f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_01a03483-6d09-70f6-81d3-21b9a35f5af3" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_01a03483-6d09-75a3-8747-302349a8624f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_01a03483-6d09-727e-8acd-a6ae49c23e09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_01a03483-6d09-70f6-81d3-21b9a35f5af3" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_01a03483-6d09-727e-8acd-a6ae49c23e09" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/AcquisitionsDetails" xlink:type="simple" xlink:href="pnr-20260930.xsd#AcquisitionsDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/AcquisitionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_01a03483-6d09-78e9-98ec-be493cc6149c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a03483-6d09-72f4-981c-bc8b92ba215c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a03483-6d09-78e9-98ec-be493cc6149c" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a03483-6d09-72f4-981c-bc8b92ba215c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_01a03483-6d09-78f5-bec7-aad1883ad7fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a03483-6d09-72f4-981c-bc8b92ba215c" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_01a03483-6d09-78f5-bec7-aad1883ad7fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a03483-6d09-78f5-bec7-aad1883ad7fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a03483-6d09-78f5-bec7-aad1883ad7fc" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a03483-6d09-78f5-bec7-aad1883ad7fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a03483-6d09-730b-b655-402d3af4ae17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a03483-6d09-78f5-bec7-aad1883ad7fc" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a03483-6d09-730b-b655-402d3af4ae17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TacoMember_01a159f1-bee8-736a-9e27-bc3af0b2ac98" xlink:href="pnr-20260930.xsd#pnr_TacoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a03483-6d09-730b-b655-402d3af4ae17" xlink:to="loc_pnr_TacoMember_01a159f1-bee8-736a-9e27-bc3af0b2ac98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_01a159f1-bee8-744b-b940-108ea01f210e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a03483-6d09-72f4-981c-bc8b92ba215c" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_01a159f1-bee8-744b-b940-108ea01f210e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a159f1-bee8-744b-b940-108ea01f210e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a159f1-bee8-744b-b940-108ea01f210e" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a159f1-bee8-744b-b940-108ea01f210e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a159f1-bee8-7e92-a978-dba95ec2b0ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a159f1-bee8-744b-b940-108ea01f210e" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a159f1-bee8-7e92-a978-dba95ec2b0ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_01a159f1-bee8-7f78-8e1f-f9d203a6b17b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_01a159f1-bee8-7e92-a978-dba95ec2b0ff" xlink:to="loc_us-gaap_SubsequentEventMember_01a159f1-bee8-7f78-8e1f-f9d203a6b17b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_01a03483-6d09-7f9f-8d11-04bce460b3c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a03483-6d09-78e9-98ec-be493cc6149c" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_01a03483-6d09-7f9f-8d11-04bce460b3c1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SharePlansScheduleofSharebasedCompensationExpenseDetails" xlink:type="simple" xlink:href="pnr-20260930.xsd#SharePlansScheduleofSharebasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SharePlansScheduleofSharebasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-71ce-b5bf-f9d4ff3e1b68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03483-6d09-77f8-98bd-8835f0d8d9ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-71ce-b5bf-f9d4ff3e1b68" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03483-6d09-77f8-98bd-8835f0d8d9ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a03483-6d09-7f5a-bc52-81f7f239c160" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03483-6d09-77f8-98bd-8835f0d8d9ff" xlink:to="loc_us-gaap_AwardTypeAxis_01a03483-6d09-7f5a-bc52-81f7f239c160" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7f5a-bc52-81f7f239c160_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a03483-6d09-7f5a-bc52-81f7f239c160" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7f5a-bc52-81f7f239c160_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7977-abb6-40b85db46c27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a03483-6d09-7f5a-bc52-81f7f239c160" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7977-abb6-40b85db46c27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a03483-6d09-73e6-952b-74aaf371b3a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7977-abb6-40b85db46c27" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a03483-6d09-73e6-952b-74aaf371b3a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockOptionMember_01a03483-6d09-72ba-9779-4bc798d5b3d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7977-abb6-40b85db46c27" xlink:to="loc_us-gaap_StockOptionMember_01a03483-6d09-72ba-9779-4bc798d5b3d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_01a03483-6d09-7af0-8716-b085b2bdac1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7977-abb6-40b85db46c27" xlink:to="loc_us-gaap_PerformanceSharesMember_01a03483-6d09-7af0-8716-b085b2bdac1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_01a03483-6d09-7ac7-b7a2-b59978d564da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-71ce-b5bf-f9d4ff3e1b68" xlink:to="loc_us-gaap_ShareBasedCompensation_01a03483-6d09-7ac7-b7a2-b59978d564da" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SharePlansAdditionalInformationDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#SharePlansAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SharePlansAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-7866-b562-dbe301371006" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03483-6d09-70c4-a84d-0c1b5e3e5727" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-7866-b562-dbe301371006" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03483-6d09-70c4-a84d-0c1b5e3e5727" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_01a03483-6d09-7d03-9946-6458fa7521ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03483-6d09-70c4-a84d-0c1b5e3e5727" xlink:to="loc_us-gaap_PlanNameAxis_01a03483-6d09-7d03-9946-6458fa7521ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a03483-6d09-7d03-9946-6458fa7521ed_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_01a03483-6d09-7d03-9946-6458fa7521ed" xlink:to="loc_us-gaap_PlanNameDomain_01a03483-6d09-7d03-9946-6458fa7521ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a03483-6d09-7b72-9a04-3edd26057398" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_01a03483-6d09-7d03-9946-6458fa7521ed" xlink:to="loc_us-gaap_PlanNameDomain_01a03483-6d09-7b72-9a04-3edd26057398" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TwoThousandTwentyShareAndIncentivePlanMember_01a03483-6d09-708e-ac63-c782df649ab1" xlink:href="pnr-20260930.xsd#pnr_TwoThousandTwentyShareAndIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a03483-6d09-7b72-9a04-3edd26057398" xlink:to="loc_pnr_TwoThousandTwentyShareAndIncentivePlanMember_01a03483-6d09-708e-ac63-c782df649ab1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a03483-6d09-7d92-b492-7d570953d3e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03483-6d09-70c4-a84d-0c1b5e3e5727" xlink:to="loc_us-gaap_AwardTypeAxis_01a03483-6d09-7d92-b492-7d570953d3e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7d92-b492-7d570953d3e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a03483-6d09-7d92-b492-7d570953d3e1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-7d92-b492-7d570953d3e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-79fd-b250-e9dfcf4209a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a03483-6d09-7d92-b492-7d570953d3e1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-79fd-b250-e9dfcf4209a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a03483-6d09-7dfa-a19e-fa7ae19df1f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-79fd-b250-e9dfcf4209a8" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a03483-6d09-7dfa-a19e-fa7ae19df1f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockOptionMember_01a03483-6d09-72f6-8fae-d3d5c3a89a75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-79fd-b250-e9dfcf4209a8" xlink:to="loc_us-gaap_StockOptionMember_01a03483-6d09-72f6-8fae-d3d5c3a89a75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_01a03483-6d09-74f8-a351-229a40d28250" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03483-6d09-79fd-b250-e9dfcf4209a8" xlink:to="loc_us-gaap_PerformanceSharesMember_01a03483-6d09-74f8-a351-229a40d28250" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_01a03483-6d09-7956-968d-0a250a8a9ed1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-7866-b562-dbe301371006" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_01a03483-6d09-7956-968d-0a250a8a9ed1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a03483-6d09-73be-b19c-e8020e1d7a55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-7866-b562-dbe301371006" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a03483-6d09-73be-b19c-e8020e1d7a55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_01a03483-6d09-7dd4-a9ed-28b9dfd3d6ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-7866-b562-dbe301371006" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_01a03483-6d09-7dd4-a9ed-28b9dfd3d6ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a03483-6d09-71ca-8318-77889a2a487d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-7866-b562-dbe301371006" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a03483-6d09-71ca-8318-77889a2a487d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a03483-6d09-7251-88fd-1e9043c42473" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03483-6d09-7866-b562-dbe301371006" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a03483-6d09-7251-88fd-1e9043c42473" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/RestructuringandTransformationProgramCostsIncludedinSellingGeneralAdministrativeExpensesDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#RestructuringandTransformationProgramCostsIncludedinSellingGeneralAdministrativeExpensesDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/RestructuringandTransformationProgramCostsIncludedinSellingGeneralAdministrativeExpensesDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_01a03483-6d09-7844-a5d0-de561094f4e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a03483-6d09-7987-9706-0bc625bad008" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a03483-6d09-7844-a5d0-de561094f4e5" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a03483-6d09-7987-9706-0bc625bad008" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_01a03483-6d09-78d8-a0c5-f5757dd6840e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a03483-6d09-7987-9706-0bc625bad008" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_01a03483-6d09-78d8-a0c5-f5757dd6840e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_01a03483-6d09-78d8-a0c5-f5757dd6840e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_01a03483-6d09-78d8-a0c5-f5757dd6840e" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_01a03483-6d09-78d8-a0c5-f5757dd6840e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_01a03483-6d09-7dce-a83b-f03896872ad7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_01a03483-6d09-78d8-a0c5-f5757dd6840e" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_01a03483-6d09-7dce-a83b-f03896872ad7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeveranceAndRelatedCostsMember_01a03483-6d09-7373-9d12-9542bfc5fbd5" xlink:href="pnr-20260930.xsd#pnr_SeveranceAndRelatedCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_01a03483-6d09-7dce-a83b-f03896872ad7" xlink:to="loc_pnr_SeveranceAndRelatedCostsMember_01a03483-6d09-7373-9d12-9542bfc5fbd5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_01a03483-6d09-7f42-bc41-3ad61bf23c2b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_01a03483-6d09-7dce-a83b-f03896872ad7" xlink:to="loc_us-gaap_OtherRestructuringMember_01a03483-6d09-7f42-bc41-3ad61bf23c2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_AssetImpairmentsAndWriteOffsMember_01a03483-6d09-7976-b5cd-521bb5fc813a" xlink:href="pnr-20260930.xsd#pnr_AssetImpairmentsAndWriteOffsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_01a03483-6d09-7dce-a83b-f03896872ad7" xlink:to="loc_pnr_AssetImpairmentsAndWriteOffsMember_01a03483-6d09-7976-b5cd-521bb5fc813a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationTypeAxis_01a03483-6d09-7c2f-878c-96493b8511eb" xlink:href="pnr-20260930.xsd#pnr_TransformationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a03483-6d09-7987-9706-0bc625bad008" xlink:to="loc_pnr_TransformationTypeAxis_01a03483-6d09-7c2f-878c-96493b8511eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationTypeDomain_01a03483-6d09-7c2f-878c-96493b8511eb_default" xlink:href="pnr-20260930.xsd#pnr_TransformationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pnr_TransformationTypeAxis_01a03483-6d09-7c2f-878c-96493b8511eb" xlink:to="loc_pnr_TransformationTypeDomain_01a03483-6d09-7c2f-878c-96493b8511eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationTypeDomain_01a03483-6d09-7909-924f-83e95a436b27" xlink:href="pnr-20260930.xsd#pnr_TransformationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pnr_TransformationTypeAxis_01a03483-6d09-7c2f-878c-96493b8511eb" xlink:to="loc_pnr_TransformationTypeDomain_01a03483-6d09-7909-924f-83e95a436b27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeveranceAndRelatedCostsMember_01a03483-6d09-7943-af8b-4aa106bbb451" xlink:href="pnr-20260930.xsd#pnr_SeveranceAndRelatedCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_TransformationTypeDomain_01a03483-6d09-7909-924f-83e95a436b27" xlink:to="loc_pnr_SeveranceAndRelatedCostsMember_01a03483-6d09-7943-af8b-4aa106bbb451" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_AssetImpairmentsAndWriteOffsMember_01a03483-6d09-7cd2-aaaa-bef6e046cf00" xlink:href="pnr-20260930.xsd#pnr_AssetImpairmentsAndWriteOffsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_TransformationTypeDomain_01a03483-6d09-7909-924f-83e95a436b27" xlink:to="loc_pnr_AssetImpairmentsAndWriteOffsMember_01a03483-6d09-7cd2-aaaa-bef6e046cf00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherTransformationMember_01a03483-6d09-75f8-903c-8a11964914a7" xlink:href="pnr-20260930.xsd#pnr_OtherTransformationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_TransformationTypeDomain_01a03483-6d09-7909-924f-83e95a436b27" xlink:to="loc_pnr_OtherTransformationMember_01a03483-6d09-75f8-903c-8a11964914a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_01a03483-6d09-7be5-b99b-99beea6a16ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a03483-6d09-7844-a5d0-de561094f4e5" xlink:to="loc_us-gaap_RestructuringCharges_01a03483-6d09-7be5-b99b-99beea6a16ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationCosts_01a03483-6d09-7f25-a102-878c9c1e8fdf" xlink:href="pnr-20260930.xsd#pnr_TransformationCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a03483-6d09-7844-a5d0-de561094f4e5" xlink:to="loc_pnr_TransformationCosts_01a03483-6d09-7f25-a102-878c9c1e8fdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TotalRestructuringAndTransformationCosts_01a03483-6d09-787d-8ffe-03511973fdf2" xlink:href="pnr-20260930.xsd#pnr_TotalRestructuringAndTransformationCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a03483-6d09-7844-a5d0-de561094f4e5" xlink:to="loc_pnr_TotalRestructuringAndTransformationCosts_01a03483-6d09-787d-8ffe-03511973fdf2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/RestructuringandTransformationProgramRestructuringCostsbySegmentDetails" xlink:type="simple" xlink:href="pnr-20260930.xsd#RestructuringandTransformationProgramRestructuringCostsbySegmentDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/RestructuringandTransformationProgramRestructuringCostsbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_01a03483-6d09-7838-869a-22812c4fed36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a03483-6d09-7514-9802-199cb4c4aa3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a03483-6d09-7838-869a-22812c4fed36" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a03483-6d09-7514-9802-199cb4c4aa3f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-7c64-b596-a12be4974ce5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a03483-6d09-7514-9802-199cb4c4aa3f" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-7c64-b596-a12be4974ce5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03483-6d09-7c64-b596-a12be4974ce5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-7c64-b596-a12be4974ce5" xlink:to="loc_us-gaap_SegmentDomain_01a03483-6d09-7c64-b596-a12be4974ce5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03483-6d09-74e7-9c4a-36e1abd5ae53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-7c64-b596-a12be4974ce5" xlink:to="loc_us-gaap_SegmentDomain_01a03483-6d09-74e7-9c4a-36e1abd5ae53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_FlowMember_01a03483-6d09-7cc3-a8e7-b6e08cf72879" xlink:href="pnr-20260930.xsd#pnr_FlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-74e7-9c4a-36e1abd5ae53" xlink:to="loc_pnr_FlowMember_01a03483-6d09-7cc3-a8e7-b6e08cf72879" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WaterSolutionsMember_01a03483-6d09-7476-a190-2dd466f4688b" xlink:href="pnr-20260930.xsd#pnr_WaterSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-74e7-9c4a-36e1abd5ae53" xlink:to="loc_pnr_WaterSolutionsMember_01a03483-6d09-7476-a190-2dd466f4688b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PoolMember_01a03483-6d09-76c7-b1c4-dbf5f80ec24a" xlink:href="pnr-20260930.xsd#pnr_PoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-74e7-9c4a-36e1abd5ae53" xlink:to="loc_pnr_PoolMember_01a03483-6d09-76c7-b1c4-dbf5f80ec24a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a03483-6d09-74cb-8bec-eb8c5f575705" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a03483-6d09-7514-9802-199cb4c4aa3f" xlink:to="loc_srt_ConsolidationItemsAxis_01a03483-6d09-74cb-8bec-eb8c5f575705" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a03483-6d09-74cb-8bec-eb8c5f575705_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_01a03483-6d09-74cb-8bec-eb8c5f575705" xlink:to="loc_srt_ConsolidationItemsDomain_01a03483-6d09-74cb-8bec-eb8c5f575705_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a03483-6d09-7a48-b410-5136c8caeccf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_01a03483-6d09-74cb-8bec-eb8c5f575705" xlink:to="loc_srt_ConsolidationItemsDomain_01a03483-6d09-7a48-b410-5136c8caeccf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_01a03483-6d09-7009-9799-068df6bfb6b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a03483-6d09-7a48-b410-5136c8caeccf" xlink:to="loc_us-gaap_OperatingSegmentsMember_01a03483-6d09-7009-9799-068df6bfb6b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_01a03483-6d09-7fcc-baea-8071aa9de254" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a03483-6d09-7a48-b410-5136c8caeccf" xlink:to="loc_us-gaap_CorporateNonSegmentMember_01a03483-6d09-7fcc-baea-8071aa9de254" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TotalRestructuringAndTransformationCosts_01a03483-6d09-7823-8099-4b133814579a" xlink:href="pnr-20260930.xsd#pnr_TotalRestructuringAndTransformationCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a03483-6d09-7838-869a-22812c4fed36" xlink:to="loc_pnr_TotalRestructuringAndTransformationCosts_01a03483-6d09-7823-8099-4b133814579a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SupplementalBalanceSheetInformationDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#SupplementalBalanceSheetInformationDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SupplementalBalanceSheetInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a03483-6d09-762f-b161-25b310cae1d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a03483-6d09-7bfc-99b3-c15b6bd258ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a03483-6d09-762f-b161-25b310cae1d8" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a03483-6d09-7bfc-99b3-c15b6bd258ab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a03483-6d09-788d-a41d-8a4b8bf01212" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a03483-6d09-7bfc-99b3-c15b6bd258ab" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a03483-6d09-788d-a41d-8a4b8bf01212" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-788d-a41d-8a4b8bf01212_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a03483-6d09-788d-a41d-8a4b8bf01212" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-788d-a41d-8a4b8bf01212_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-7be1-9ec4-15148d02aac3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a03483-6d09-788d-a41d-8a4b8bf01212" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-7be1-9ec4-15148d02aac3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandAndLandImprovementsMember_01a03483-6d09-7113-9953-426ff2c14ed2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandAndLandImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-7be1-9ec4-15148d02aac3" xlink:to="loc_us-gaap_LandAndLandImprovementsMember_01a03483-6d09-7113-9953-426ff2c14ed2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_01a03483-6d09-74f2-9f84-bb635d0ab4aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-7be1-9ec4-15148d02aac3" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_01a03483-6d09-74f2-9f84-bb635d0ab4aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_01a03483-6d09-70d8-9b61-7dfd29f4c092" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-7be1-9ec4-15148d02aac3" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_01a03483-6d09-70d8-9b61-7dfd29f4c092" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_01a03483-6d09-7027-bdd6-39b675bf55bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-7be1-9ec4-15148d02aac3" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_01a03483-6d09-7027-bdd6-39b675bf55bb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_01a03483-6d09-74ca-b506-2ba53517cc7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a03483-6d09-7be1-9ec4-15148d02aac3" xlink:to="loc_us-gaap_ConstructionInProgressMember_01a03483-6d09-74ca-b506-2ba53517cc7e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNetAbstract_01a03483-6d09-7494-b987-53311b0063ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a03483-6d09-762f-b161-25b310cae1d8" xlink:to="loc_us-gaap_InventoryNetAbstract_01a03483-6d09-7494-b987-53311b0063ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryRawMaterialsAndSupplies_01a03483-6d09-71ce-935a-d3040f4d8c53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryRawMaterialsAndSupplies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryNetAbstract_01a03483-6d09-7494-b987-53311b0063ed" xlink:to="loc_us-gaap_InventoryRawMaterialsAndSupplies_01a03483-6d09-71ce-935a-d3040f4d8c53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWorkInProcess_01a03483-6d09-7a3f-a457-da6d3cf3e2ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryWorkInProcess"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryNetAbstract_01a03483-6d09-7494-b987-53311b0063ed" xlink:to="loc_us-gaap_InventoryWorkInProcess_01a03483-6d09-7a3f-a457-da6d3cf3e2ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryFinishedGoods_01a03483-6d09-7309-b46e-3e23ff44a5e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryFinishedGoods"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryNetAbstract_01a03483-6d09-7494-b987-53311b0063ed" xlink:to="loc_us-gaap_InventoryFinishedGoods_01a03483-6d09-7309-b46e-3e23ff44a5e2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_01a03483-6d09-7ed0-bc24-7ddaf2800249" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryNetAbstract_01a03483-6d09-7494-b987-53311b0063ed" xlink:to="loc_us-gaap_InventoryNet_01a03483-6d09-7ed0-bc24-7ddaf2800249" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract_01a03483-6d09-7456-81ee-1b104da5604b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a03483-6d09-762f-b161-25b310cae1d8" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract_01a03483-6d09-7456-81ee-1b104da5604b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_01a03483-6d09-7b0e-882e-3e012d9de984" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract_01a03483-6d09-7456-81ee-1b104da5604b" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_01a03483-6d09-7b0e-882e-3e012d9de984" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPrepaidExpenseCurrent_01a03483-6d09-7f47-9d1a-06832f2f2148" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherPrepaidExpenseCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract_01a03483-6d09-7456-81ee-1b104da5604b" xlink:to="loc_us-gaap_OtherPrepaidExpenseCurrent_01a03483-6d09-7f47-9d1a-06832f2f2148" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherCurrentAssets_01a03483-6d09-7a9e-9786-7b099441f9d0" xlink:href="pnr-20260930.xsd#pnr_OtherCurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract_01a03483-6d09-7456-81ee-1b104da5604b" xlink:to="loc_pnr_OtherCurrentAssets_01a03483-6d09-7a9e-9786-7b099441f9d0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_01a03483-6d09-7be2-94f8-ef77ba3d31e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract_01a03483-6d09-7456-81ee-1b104da5604b" xlink:to="loc_us-gaap_OtherAssetsCurrent_01a03483-6d09-7be2-94f8-ef77ba3d31e7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAbstract_01a03483-6d09-768f-a040-6a84a66e26e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a03483-6d09-762f-b161-25b310cae1d8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAbstract_01a03483-6d09-768f-a040-6a84a66e26e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_01a03483-6d09-7aa1-a9c6-39f203bf3859" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentAbstract_01a03483-6d09-768f-a040-6a84a66e26e9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_01a03483-6d09-7aa1-a9c6-39f203bf3859" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_01a03483-6d09-7aab-b054-fec4c2c2bc1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentAbstract_01a03483-6d09-768f-a040-6a84a66e26e9" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_01a03483-6d09-7aab-b054-fec4c2c2bc1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_01a03483-6d09-79fc-8a3a-e61a8afaa2bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentAbstract_01a03483-6d09-768f-a040-6a84a66e26e9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_01a03483-6d09-79fc-8a3a-e61a8afaa2bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrentAbstract_01a03483-6d09-70b7-a61a-0929491a1082" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a03483-6d09-762f-b161-25b310cae1d8" xlink:to="loc_us-gaap_OtherAssetsNoncurrentAbstract_01a03483-6d09-70b7-a61a-0929491a1082" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_01a03483-6d09-779c-bb77-a322304c507b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_01a03483-6d09-70b7-a61a-0929491a1082" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_01a03483-6d09-779c-bb77-a322304c507b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_01a03483-6d09-79e5-914c-37aa7d8ca453" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_01a03483-6d09-70b7-a61a-0929491a1082" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_01a03483-6d09-79e5-914c-37aa7d8ca453" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationPlanAssets_01a03483-6d09-7fb0-86bb-f3e23e751f48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCompensationPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_01a03483-6d09-70b7-a61a-0929491a1082" xlink:to="loc_us-gaap_DeferredCompensationPlanAssets_01a03483-6d09-7fb0-86bb-f3e23e751f48" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherLongTermAssets_01a03483-6d09-725c-b8b4-99dca362c170" xlink:href="pnr-20260930.xsd#pnr_OtherLongTermAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_01a03483-6d09-70b7-a61a-0929491a1082" xlink:to="loc_pnr_OtherLongTermAssets_01a03483-6d09-725c-b8b4-99dca362c170" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsMiscellaneousNoncurrent_01a03483-6d09-705d-8d1d-2533c691c33f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsMiscellaneousNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_01a03483-6d09-70b7-a61a-0929491a1082" xlink:to="loc_us-gaap_OtherAssetsMiscellaneousNoncurrent_01a03483-6d09-705d-8d1d-2533c691c33f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a03483-6d09-762f-b161-25b310cae1d8" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrent_01a03483-6d09-72ac-92b9-b52ce6625cdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_DividendsPayableCurrent_01a03483-6d09-72ac-92b9-b52ce6625cdc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductWarrantyAccrualClassifiedCurrent_01a03483-6d09-7737-ba4d-17760b966a45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductWarrantyAccrualClassifiedCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_ProductWarrantyAccrualClassifiedCurrent_01a03483-6d09-7737-ba4d-17760b966a45" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedExchangeFeeRebateCurrentAndNoncurrent_01a03483-6d09-7c9a-93a1-8d677c1b102c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedExchangeFeeRebateCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_AccruedExchangeFeeRebateCurrentAndNoncurrent_01a03483-6d09-7c9a-93a1-8d677c1b102c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_AccruedFreight_01a03483-6d09-732d-b2ff-f4c8f1d2b2a6" xlink:href="pnr-20260930.xsd#pnr_AccruedFreight"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_pnr_AccruedFreight_01a03483-6d09-732d-b2ff-f4c8f1d2b2a6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a03483-6d09-7357-93d5-07615e956d11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a03483-6d09-7357-93d5-07615e956d11" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_01a03483-6d09-78d9-a55f-052437b9ac1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_01a03483-6d09-78d9-a55f-052437b9ac1f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_01a03483-6d09-7aa6-a73e-ff4dcf5822ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_01a03483-6d09-7aa6-a73e-ff4dcf5822ef" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_01a03483-6d09-7e8b-8b65-0d0c813a8d54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_RestructuringReserve_01a03483-6d09-7e8b-8b65-0d0c813a8d54" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrentAndNoncurrent_01a03483-6d09-7987-8b62-161e2ace590a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_InterestPayableCurrentAndNoncurrent_01a03483-6d09-7987-8b62-161e2ace590a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_01a03483-6d09-7465-bba6-d95d97fb6f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_01a03483-6d09-7465-bba6-d95d97fb6f5f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_01a03483-6d09-7496-9778-62addc1b5e6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a03483-6d09-7005-9bc2-7ee4557a9cb0" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_01a03483-6d09-7496-9778-62addc1b5e6b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a03483-6d09-762f-b161-25b310cae1d8" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_01a03483-6d09-7be1-9939-e4707be10331" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_01a03483-6d09-7be1-9939-e4707be10331" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesNoncurrent_01a03483-6d09-785c-9653-8065ed343fa9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedIncomeTaxesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:to="loc_us-gaap_AccruedIncomeTaxesNoncurrent_01a03483-6d09-785c-9653-8065ed343fa9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SelfInsuranceReserveNoncurrent_01a03483-6d09-73dc-9663-bed22598301d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SelfInsuranceReserveNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:to="loc_us-gaap_SelfInsuranceReserveNoncurrent_01a03483-6d09-73dc-9663-bed22598301d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationLiabilityCurrent_01a03483-6d09-767b-a0de-8038d3276370" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCompensationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:to="loc_us-gaap_DeferredCompensationLiabilityCurrent_01a03483-6d09-767b-a0de-8038d3276370" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_01a03483-6d09-779d-8d3a-80711c173c12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:to="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_01a03483-6d09-779d-8d3a-80711c173c12" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherLongTermLiabilities_01a03483-6d09-7ddd-8312-33e84a29a357" xlink:href="pnr-20260930.xsd#pnr_OtherLongTermLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:to="loc_pnr_OtherLongTermLiabilities_01a03483-6d09-7ddd-8312-33e84a29a357" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_01a03483-6d09-7acd-9aef-b6da7aa17274" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_01a03483-6d09-7ba5-b9de-299cd7042d0f" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_01a03483-6d09-7acd-9aef-b6da7aa17274" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/GoodwillandOtherIdentifiableIntangibleAssetsChangesinCarryingAmountofGoodwillbySegmentDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#GoodwillandOtherIdentifiableIntangibleAssetsChangesinCarryingAmountofGoodwillbySegmentDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/GoodwillandOtherIdentifiableIntangibleAssetsChangesinCarryingAmountofGoodwillbySegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_01a03483-6d09-7783-80ef-c4a40375a286" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_01a03483-6d09-784a-a21b-96d7b8511bd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_01a03483-6d09-7783-80ef-c4a40375a286" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_01a03483-6d09-784a-a21b-96d7b8511bd9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-7f1c-9769-813a2f3af632" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_01a03483-6d09-784a-a21b-96d7b8511bd9" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-7f1c-9769-813a2f3af632" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03483-6d09-7f1c-9769-813a2f3af632_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-7f1c-9769-813a2f3af632" xlink:to="loc_us-gaap_SegmentDomain_01a03483-6d09-7f1c-9769-813a2f3af632_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03483-6d09-7e4c-9058-9de9bfecea8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-7f1c-9769-813a2f3af632" xlink:to="loc_us-gaap_SegmentDomain_01a03483-6d09-7e4c-9058-9de9bfecea8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_FlowMember_01a03483-6d09-7018-ade8-b151e49b2dc4" xlink:href="pnr-20260930.xsd#pnr_FlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-7e4c-9058-9de9bfecea8f" xlink:to="loc_pnr_FlowMember_01a03483-6d09-7018-ade8-b151e49b2dc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WaterSolutionsMember_01a03483-6d09-7a59-a273-43e9ff3ba124" xlink:href="pnr-20260930.xsd#pnr_WaterSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-7e4c-9058-9de9bfecea8f" xlink:to="loc_pnr_WaterSolutionsMember_01a03483-6d09-7a59-a273-43e9ff3ba124" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PoolMember_01a03483-6d09-783b-b10d-be31dddf738a" xlink:href="pnr-20260930.xsd#pnr_PoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-7e4c-9058-9de9bfecea8f" xlink:to="loc_pnr_PoolMember_01a03483-6d09-783b-b10d-be31dddf738a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_01a03483-6d09-7c88-9d46-8063c04d6a94" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_01a03483-6d09-784a-a21b-96d7b8511bd9" xlink:to="loc_srt_RestatementAxis_01a03483-6d09-7c88-9d46-8063c04d6a94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a03483-6d09-7c88-9d46-8063c04d6a94_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_01a03483-6d09-7c88-9d46-8063c04d6a94" xlink:to="loc_srt_RestatementDomain_01a03483-6d09-7c88-9d46-8063c04d6a94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_01a03483-6d09-70be-bad8-e1cda42204a3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_01a03483-6d09-7c88-9d46-8063c04d6a94" xlink:to="loc_srt_RestatementDomain_01a03483-6d09-70be-bad8-e1cda42204a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_01a03483-6d09-7f99-9d90-4f2075779f7d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a03483-6d09-70be-bad8-e1cda42204a3" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_01a03483-6d09-7f99-9d90-4f2075779f7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInReportingEntityAdjustmentMember_01a03483-6d09-7fe2-b8cb-a51bc433cbb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ChangeInReportingEntityAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_01a03483-6d09-70be-bad8-e1cda42204a3" xlink:to="loc_us-gaap_ChangeInReportingEntityAdjustmentMember_01a03483-6d09-7fe2-b8cb-a51bc433cbb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeAxis_01a03483-6d09-7ee8-aff0-55fc7bafde39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_01a03483-6d09-784a-a21b-96d7b8511bd9" xlink:to="loc_us-gaap_ReclassificationTypeAxis_01a03483-6d09-7ee8-aff0-55fc7bafde39" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeDomain_01a03483-6d09-7ee8-aff0-55fc7bafde39_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationTypeAxis_01a03483-6d09-7ee8-aff0-55fc7bafde39" xlink:to="loc_us-gaap_ReclassificationTypeDomain_01a03483-6d09-7ee8-aff0-55fc7bafde39_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeDomain_01a03483-6d09-7b21-be5c-94d5ac6812d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationTypeAxis_01a03483-6d09-7ee8-aff0-55fc7bafde39" xlink:to="loc_us-gaap_ReclassificationTypeDomain_01a03483-6d09-7b21-be5c-94d5ac6812d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ReclassificationFairValueImpactMember_01a03483-6d09-7bed-91ee-b0002f9e9bf5" xlink:href="pnr-20260930.xsd#pnr_ReclassificationFairValueImpactMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationTypeDomain_01a03483-6d09-7b21-be5c-94d5ac6812d8" xlink:to="loc_pnr_ReclassificationFairValueImpactMember_01a03483-6d09-7bed-91ee-b0002f9e9bf5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationSegmentationBasisChangeMember_01a03483-6d09-73d1-bd68-5b220a51ba6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationSegmentationBasisChangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationTypeDomain_01a03483-6d09-7b21-be5c-94d5ac6812d8" xlink:to="loc_us-gaap_ReclassificationSegmentationBasisChangeMember_01a03483-6d09-73d1-bd68-5b220a51ba6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_01a03483-6d09-7f6d-b0c5-b3929d4ed8e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_01a03483-6d09-7783-80ef-c4a40375a286" xlink:to="loc_us-gaap_GoodwillRollForward_01a03483-6d09-7f6d-b0c5-b3929d4ed8e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_01a03483-6d09-7c3a-960d-ce8c5850865c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_01a03483-6d09-7f6d-b0c5-b3929d4ed8e3" xlink:to="loc_us-gaap_Goodwill_01a03483-6d09-7c3a-960d-ce8c5850865c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillOtherIncreaseDecrease_01a03483-6d09-7600-81db-0e1f3b60d006" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillOtherIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_01a03483-6d09-7f6d-b0c5-b3929d4ed8e3" xlink:to="loc_us-gaap_GoodwillOtherIncreaseDecrease_01a03483-6d09-7600-81db-0e1f3b60d006" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_01a03483-6d09-74c4-8f01-8892bf3790b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/GoodwillandOtherIdentifiableIntangibleAssetsDetailofIdentifiableIntangibleAssetsDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#GoodwillandOtherIdentifiableIntangibleAssetsDetailofIdentifiableIntangibleAssetsDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/GoodwillandOtherIdentifiableIntangibleAssetsDetailofIdentifiableIntangibleAssetsDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_01a03483-6d09-7eb3-8c04-c63e01912ba3" xlink:href="pnr-20260930.xsd#pnr_AcquiredIntangibleAssetsByMajorClassLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable_01a03483-6d09-7a8b-9c05-fbbfb955d161" xlink:href="pnr-20260930.xsd#pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_01a03483-6d09-7eb3-8c04-c63e01912ba3" xlink:to="loc_pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable_01a03483-6d09-7a8b-9c05-fbbfb955d161" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a03483-6d09-74ef-a3cb-6c414df6d187" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable_01a03483-6d09-7a8b-9c05-fbbfb955d161" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a03483-6d09-74ef-a3cb-6c414df6d187" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-74ef-a3cb-6c414df6d187_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a03483-6d09-74ef-a3cb-6c414df6d187" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-74ef-a3cb-6c414df6d187_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-7f19-ac33-6fcf4428d259" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a03483-6d09-74ef-a3cb-6c414df6d187" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-7f19-ac33-6fcf4428d259" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_01a03483-6d09-73c0-942d-4aba4c4abed5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-7f19-ac33-6fcf4428d259" xlink:to="loc_us-gaap_CustomerRelationshipsMember_01a03483-6d09-73c0-942d-4aba4c4abed5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntellectualPropertyMember_01a03483-6d09-7135-93df-cda940096877" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-7f19-ac33-6fcf4428d259" xlink:to="loc_us-gaap_IntellectualPropertyMember_01a03483-6d09-7135-93df-cda940096877" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01a03483-6d09-76cf-ad99-fc2222f208d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_ScheduleOfAcquiredIntangibleAssetsByMajorClassTable_01a03483-6d09-7a8b-9c05-fbbfb955d161" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01a03483-6d09-76cf-ad99-fc2222f208d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-76cf-ad99-fc2222f208d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01a03483-6d09-76cf-ad99-fc2222f208d8" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-76cf-ad99-fc2222f208d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-7fd6-8ac4-80eea1c628b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01a03483-6d09-76cf-ad99-fc2222f208d8" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-7fd6-8ac4-80eea1c628b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_01a03483-6d09-7f8d-852a-cd4a6fdd15ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a03483-6d09-7fd6-8ac4-80eea1c628b6" xlink:to="loc_us-gaap_TradeNamesMember_01a03483-6d09-7f8d-852a-cd4a6fdd15ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a03483-6d09-7af5-992a-968bb60afc57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_01a03483-6d09-7eb3-8c04-c63e01912ba3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a03483-6d09-7af5-992a-968bb60afc57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a03483-6d09-7a3b-b672-90ed1948a879" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_01a03483-6d09-7eb3-8c04-c63e01912ba3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a03483-6d09-7a3b-b672-90ed1948a879" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a03483-6d09-7069-8bf2-0994b6d3ce12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_01a03483-6d09-7eb3-8c04-c63e01912ba3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a03483-6d09-7069-8bf2-0994b6d3ce12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_01a03483-6d09-72fe-8c28-d38eeccd050b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_01a03483-6d09-7eb3-8c04-c63e01912ba3" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_01a03483-6d09-72fe-8c28-d38eeccd050b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_01a03483-6d09-722d-849f-5d64ce07ad81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_01a03483-6d09-7eb3-8c04-c63e01912ba3" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_01a03483-6d09-722d-849f-5d64ce07ad81" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a03483-6d09-7d97-9293-a9d548a59890" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_AcquiredIntangibleAssetsByMajorClassLineItems_01a03483-6d09-7eb3-8c04-c63e01912ba3" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a03483-6d09-7d97-9293-a9d548a59890" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DebtDebtandAverageInterestRatesonDebtOutstandingDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#DebtDebtandAverageInterestRatesonDebtOutstandingDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DebtDebtandAverageInterestRatesonDebtOutstandingDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7dcb-a304-ec7b34390f90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7dcb-a304-ec7b34390f90" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a03483-6d09-7f9d-92c7-0c54a0c3c457" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7dcb-a304-ec7b34390f90" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a03483-6d09-7f9d-92c7-0c54a0c3c457" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7f9d-92c7-0c54a0c3c457_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a03483-6d09-7f9d-92c7-0c54a0c3c457" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7f9d-92c7-0c54a0c3c457_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-74ef-be96-5e67365a8df4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a03483-6d09-7f9d-92c7-0c54a0c3c457" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-74ef-be96-5e67365a8df4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a03483-6d09-7a7e-8b4e-59558982b7a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-74ef-be96-5e67365a8df4" xlink:to="loc_us-gaap_LineOfCreditMember_01a03483-6d09-7a7e-8b4e-59558982b7a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TermLoansMember_01a03483-6d09-7a1a-9f96-c47257e8fb75" xlink:href="pnr-20260930.xsd#pnr_TermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-74ef-be96-5e67365a8df4" xlink:to="loc_pnr_TermLoansMember_01a03483-6d09-7a1a-9f96-c47257e8fb75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_01a03483-6d09-700f-b465-758c42f4d9ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-74ef-be96-5e67365a8df4" xlink:to="loc_us-gaap_SeniorNotesMember_01a03483-6d09-700f-b465-758c42f4d9ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a03483-6d09-7f8a-bb8c-9d28f20ae2b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7dcb-a304-ec7b34390f90" xlink:to="loc_us-gaap_CreditFacilityAxis_01a03483-6d09-7f8a-bb8c-9d28f20ae2b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-7f8a-bb8c-9d28f20ae2b3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a03483-6d09-7f8a-bb8c-9d28f20ae2b3" xlink:to="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-7f8a-bb8c-9d28f20ae2b3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-7159-b717-8099af9c42c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a03483-6d09-7f8a-bb8c-9d28f20ae2b3" xlink:to="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-7159-b717-8099af9c42c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_01a03483-6d09-7350-8714-0d3610c5c56c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-7159-b717-8099af9c42c4" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_01a03483-6d09-7350-8714-0d3610c5c56c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A4YearTermLoanFacilityMember_01a03483-6d09-79ab-9b8c-64a6dd8f7eb9" xlink:href="pnr-20260930.xsd#pnr_A4YearTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-7159-b717-8099af9c42c4" xlink:to="loc_pnr_A4YearTermLoanFacilityMember_01a03483-6d09-79ab-9b8c-64a6dd8f7eb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a03483-6d09-725a-9d9d-008f74947498" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7dcb-a304-ec7b34390f90" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a03483-6d09-725a-9d9d-008f74947498" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-725a-9d9d-008f74947498_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a03483-6d09-725a-9d9d-008f74947498" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-725a-9d9d-008f74947498_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-7f56-82ae-e8e9117cbcbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a03483-6d09-725a-9d9d-008f74947498" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-7f56-82ae-e8e9117cbcbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A4YearTermLoanFacilityMember_01a03483-6d09-7ddd-897c-df3525df0626" xlink:href="pnr-20260930.xsd#pnr_A4YearTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-7f56-82ae-e8e9117cbcbb" xlink:to="loc_pnr_A4YearTermLoanFacilityMember_01a03483-6d09-7ddd-897c-df3525df0626" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A5YearTermLoanFacilityMember_01a03483-6d09-72b5-a384-11802a7f2138" xlink:href="pnr-20260930.xsd#pnr_A5YearTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-7f56-82ae-e8e9117cbcbb" xlink:to="loc_pnr_A5YearTermLoanFacilityMember_01a03483-6d09-72b5-a384-11802a7f2138" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeniorNotes4500Due2029Member_01a03483-6d09-7f19-8455-8f981357393c" xlink:href="pnr-20260930.xsd#pnr_SeniorNotes4500Due2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-7f56-82ae-e8e9117cbcbb" xlink:to="loc_pnr_SeniorNotes4500Due2029Member_01a03483-6d09-7f19-8455-8f981357393c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_SeniorNotesFivePointNinePercentDueTwentyThirtyTwoMember_01a03483-6d09-7ebf-80d2-83bc85ec77bc" xlink:href="pnr-20260930.xsd#pnr_SeniorNotesFivePointNinePercentDueTwentyThirtyTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-7f56-82ae-e8e9117cbcbb" xlink:to="loc_pnr_SeniorNotesFivePointNinePercentDueTwentyThirtyTwoMember_01a03483-6d09-7ebf-80d2-83bc85ec77bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtWeightedAverageInterestRate_01a03483-6d09-78d5-9de2-85ad5aa7c8b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_DebtWeightedAverageInterestRate_01a03483-6d09-78d5-9de2-85ad5aa7c8b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_01a03483-6d09-762d-8716-8e1d63783778" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_01a03483-6d09-762d-8716-8e1d63783778" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_01a03483-6d09-7e66-98af-d8b69c82fb02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_01a03483-6d09-7e66-98af-d8b69c82fb02" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a03483-6d09-7696-bd9c-111405509463" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_LongTermDebt_01a03483-6d09-7696-bd9c-111405509463" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a03483-6d09-72bb-81ab-ab9edc153e07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a03483-6d09-72bb-81ab-ab9edc153e07" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPayment_01a03483-6d09-7d2f-80f2-adcc968325cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentPeriodicPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPayment_01a03483-6d09-7d2f-80f2-adcc968325cd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_01a03483-6d09-7642-822b-07ccf01ef517" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_01a03483-6d09-7642-822b-07ccf01ef517" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_01a03483-6d09-7dbc-bea6-f3044dd2c741" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-7503-aee0-71a604337112" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_01a03483-6d09-7dbc-bea6-f3044dd2c741" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DebtAdditionalInformationDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#DebtAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DebtAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_01a03483-6d09-7d03-a7fb-245a674623ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:to="loc_us-gaap_LineOfCreditFacilityAxis_01a03483-6d09-7d03-a7fb-245a674623ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_01a03483-6d09-7d03-a7fb-245a674623ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_01a03483-6d09-7d03-a7fb-245a674623ff" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_01a03483-6d09-7d03-a7fb-245a674623ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_01a03483-6d09-70fc-b82e-adc04c455530" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLenderDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LineOfCreditFacilityAxis_01a03483-6d09-7d03-a7fb-245a674623ff" xlink:to="loc_us-gaap_LineOfCreditFacilityLenderDomain_01a03483-6d09-70fc-b82e-adc04c455530" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_OtherCreditFacilitiesMember_01a03483-6d09-7002-87e7-d3077fd2b250" xlink:href="pnr-20260930.xsd#pnr_OtherCreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLenderDomain_01a03483-6d09-70fc-b82e-adc04c455530" xlink:to="loc_pnr_OtherCreditFacilitiesMember_01a03483-6d09-7002-87e7-d3077fd2b250" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a03483-6d09-7c24-842a-675578958634" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a03483-6d09-7c24-842a-675578958634" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7c24-842a-675578958634_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a03483-6d09-7c24-842a-675578958634" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7c24-842a-675578958634_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7df5-9987-3428217acf78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a03483-6d09-7c24-842a-675578958634" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7df5-9987-3428217acf78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a03483-6d09-784f-b7c8-2733264c48f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7df5-9987-3428217acf78" xlink:to="loc_us-gaap_LineOfCreditMember_01a03483-6d09-784f-b7c8-2733264c48f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TermLoansMember_01a03483-6d09-78cf-921e-e3d220ef6502" xlink:href="pnr-20260930.xsd#pnr_TermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7df5-9987-3428217acf78" xlink:to="loc_pnr_TermLoansMember_01a03483-6d09-78cf-921e-e3d220ef6502" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_01a03483-6d09-7582-9bcb-b594dfc4348a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03483-6d09-7df5-9987-3428217acf78" xlink:to="loc_us-gaap_UnsecuredDebtMember_01a03483-6d09-7582-9bcb-b594dfc4348a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a03483-6d09-74b5-be93-240461010c04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:to="loc_us-gaap_CreditFacilityAxis_01a03483-6d09-74b5-be93-240461010c04" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-74b5-be93-240461010c04_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a03483-6d09-74b5-be93-240461010c04" xlink:to="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-74b5-be93-240461010c04_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-70a9-a94a-53c35f7e67e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a03483-6d09-74b5-be93-240461010c04" xlink:to="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-70a9-a94a-53c35f7e67e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_01a03483-6d09-7716-824d-477eb3d4d908" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-70a9-a94a-53c35f7e67e5" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_01a03483-6d09-7716-824d-477eb3d4d908" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BridgeLoanMember_01a15a13-fea1-7697-8248-552942830562" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BridgeLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a03483-6d09-70a9-a94a-53c35f7e67e5" xlink:to="loc_us-gaap_BridgeLoanMember_01a15a13-fea1-7697-8248-552942830562" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a03483-6d09-78b4-b75a-2ff759ad7118" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:to="loc_srt_RangeAxis_01a03483-6d09-78b4-b75a-2ff759ad7118" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03483-6d09-78b4-b75a-2ff759ad7118_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a03483-6d09-78b4-b75a-2ff759ad7118" xlink:to="loc_srt_RangeMember_01a03483-6d09-78b4-b75a-2ff759ad7118_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03483-6d09-7dbe-aca5-bab1d5dccd8f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a03483-6d09-78b4-b75a-2ff759ad7118" xlink:to="loc_srt_RangeMember_01a03483-6d09-7dbe-aca5-bab1d5dccd8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a03483-6d09-72fc-af1c-3ead07b5d6cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a03483-6d09-7dbe-aca5-bab1d5dccd8f" xlink:to="loc_srt_MinimumMember_01a03483-6d09-72fc-af1c-3ead07b5d6cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a03483-6d09-7bc2-bc39-b47ba9dd0130" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a03483-6d09-7dbe-aca5-bab1d5dccd8f" xlink:to="loc_srt_MaximumMember_01a03483-6d09-7bc2-bc39-b47ba9dd0130" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a03483-6d09-7bf1-9c91-f095f9df744e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a03483-6d09-7bf1-9c91-f095f9df744e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-7bf1-9c91-f095f9df744e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a03483-6d09-7bf1-9c91-f095f9df744e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-7bf1-9c91-f095f9df744e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-73b8-b645-1f47485ca150" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a03483-6d09-7bf1-9c91-f095f9df744e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-73b8-b645-1f47485ca150" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A4YearTermLoanFacilityMember_01a03483-6d09-73b6-b591-526e4c5bfebf" xlink:href="pnr-20260930.xsd#pnr_A4YearTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-73b8-b645-1f47485ca150" xlink:to="loc_pnr_A4YearTermLoanFacilityMember_01a03483-6d09-73b6-b591-526e4c5bfebf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TermLoansDue2023Member_01a03483-6d09-7231-b33e-a838d46258c2" xlink:href="pnr-20260930.xsd#pnr_TermLoansDue2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-73b8-b645-1f47485ca150" xlink:to="loc_pnr_TermLoansDue2023Member_01a03483-6d09-7231-b33e-a838d46258c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_Tranche1TermLoanFacilityMember_01a15a21-fd89-742b-b531-cfc5de75d7d9" xlink:href="pnr-20260930.xsd#pnr_Tranche1TermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-73b8-b645-1f47485ca150" xlink:to="loc_pnr_Tranche1TermLoanFacilityMember_01a15a21-fd89-742b-b531-cfc5de75d7d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_Tranche2TermLoanFacilityMember_01a15a1b-46ca-7825-ba34-c6ec765964b8" xlink:href="pnr-20260930.xsd#pnr_Tranche2TermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-73b8-b645-1f47485ca150" xlink:to="loc_pnr_Tranche2TermLoanFacilityMember_01a15a1b-46ca-7825-ba34-c6ec765964b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TheTermLoanFacilitiesMember_01a15a1f-be16-751d-94d8-c68379b6d16b" xlink:href="pnr-20260930.xsd#pnr_TheTermLoanFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-73b8-b645-1f47485ca150" xlink:to="loc_pnr_TheTermLoanFacilitiesMember_01a15a1f-be16-751d-94d8-c68379b6d16b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_A5YearTermLoanFacilityMember_01a03483-6d09-789d-9dbf-f2a7092d7d06" xlink:href="pnr-20260930.xsd#pnr_A5YearTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03483-6d09-73b8-b645-1f47485ca150" xlink:to="loc_pnr_A5YearTermLoanFacilityMember_01a03483-6d09-789d-9dbf-f2a7092d7d06" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a03483-6d09-7006-847f-8d5dcb31e5fd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:to="loc_srt_CounterpartyNameAxis_01a03483-6d09-7006-847f-8d5dcb31e5fd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a03483-6d09-7006-847f-8d5dcb31e5fd_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a03483-6d09-7006-847f-8d5dcb31e5fd" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a03483-6d09-7006-847f-8d5dcb31e5fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a03483-6d09-7e5d-84f8-06ff3eaa0a8f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a03483-6d09-7006-847f-8d5dcb31e5fd" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a03483-6d09-7e5d-84f8-06ff3eaa0a8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PentairPentairFinanceSRlPFSAMember_01a03483-6d09-76ce-898b-b2858b387bd8" xlink:href="pnr-20260930.xsd#pnr_PentairPentairFinanceSRlPFSAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a03483-6d09-7e5d-84f8-06ff3eaa0a8f" xlink:to="loc_pnr_PentairPentairFinanceSRlPFSAMember_01a03483-6d09-76ce-898b-b2858b387bd8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_01a03483-6d09-7b16-b1e8-a21bf44f330d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a03483-6d09-7da9-b63f-7976180a17a2" xlink:to="loc_srt_StatementScenarioAxis_01a03483-6d09-7b16-b1e8-a21bf44f330d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a03483-6d09-7b16-b1e8-a21bf44f330d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_01a03483-6d09-7b16-b1e8-a21bf44f330d" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a03483-6d09-7b16-b1e8-a21bf44f330d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a03483-6d09-755a-a58c-d0f229cef50c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_01a03483-6d09-7b16-b1e8-a21bf44f330d" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a03483-6d09-755a-a58c-d0f229cef50c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_01a03483-6d09-7fc8-8e24-940e5ef30c6f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_01a03483-6d09-755a-a58c-d0f229cef50c" xlink:to="loc_srt_ScenarioForecastMember_01a03483-6d09-7fc8-8e24-940e5ef30c6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a03483-6d09-7f19-885b-1b19cda52413" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a03483-6d09-7f19-885b-1b19cda52413" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_01a03483-6d09-72d2-8f6f-0104a5a3fbb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_01a03483-6d09-72d2-8f6f-0104a5a3fbb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_01a03483-6d09-7a07-abe8-cc7f35fbdd70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_01a03483-6d09-7a07-abe8-cc7f35fbdd70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_LineofCreditFacilityAccordionFeatureIncreaseLimit_01a03483-6d09-7a8b-95f5-93cc368f5b98" xlink:href="pnr-20260930.xsd#pnr_LineofCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_pnr_LineofCreditFacilityAccordionFeatureIncreaseLimit_01a03483-6d09-7a8b-95f5-93cc368f5b98" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPayment_01a03483-6d09-7ebd-ad93-b0b4b2dc0c63" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentPeriodicPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPayment_01a03483-6d09-7ebd-ad93-b0b4b2dc0c63" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_01a03483-6d09-7725-9060-c8797a78f947" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_01a03483-6d09-7725-9060-c8797a78f947" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_01a03483-6d09-7a2f-9748-f48280b92ee6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_01a03483-6d09-7a2f-9748-f48280b92ee6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentCovenantUnrestrictedCash_01a03483-6d09-7b95-acac-d8daa374657c" xlink:href="pnr-20260930.xsd#pnr_DebtInstrumentCovenantUnrestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_pnr_DebtInstrumentCovenantUnrestrictedCash_01a03483-6d09-7b95-acac-d8daa374657c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentLeverageRatioCovenant_01a03483-6d09-70da-b37c-cdc6caa5c7a7" xlink:href="pnr-20260930.xsd#pnr_DebtInstrumentLeverageRatioCovenant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_pnr_DebtInstrumentLeverageRatioCovenant_01a03483-6d09-70da-b37c-cdc6caa5c7a7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentLeverageRatioCovenantPeriod_01a03483-6d09-74f6-a9f0-c5ea26583b38" xlink:href="pnr-20260930.xsd#pnr_DebtInstrumentLeverageRatioCovenantPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_pnr_DebtInstrumentLeverageRatioCovenantPeriod_01a03483-6d09-74f6-a9f0-c5ea26583b38" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentCovenantNumberOfTestingPeriods_01a03483-6d09-7bb4-a595-a09f66f91ca2" xlink:href="pnr-20260930.xsd#pnr_DebtInstrumentCovenantNumberOfTestingPeriods"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_pnr_DebtInstrumentCovenantNumberOfTestingPeriods_01a03483-6d09-7bb4-a595-a09f66f91ca2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DebtInstrumentEBITDARatioCovenant_01a03483-6d09-72cc-86ee-1216b9ced5d7" xlink:href="pnr-20260930.xsd#pnr_DebtInstrumentEBITDARatioCovenant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_pnr_DebtInstrumentEBITDARatioCovenant_01a03483-6d09-72cc-86ee-1216b9ced5d7" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_01a03483-6d09-7ce4-820d-57c98eafae7f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_LineOfCredit_01a03483-6d09-7ce4-820d-57c98eafae7f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths_01a03483-6d09-7461-ab20-592d50bc7d95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a03483-6d09-72a2-82dd-0c46ef271848" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths_01a03483-6d09-7461-ab20-592d50bc7d95" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DerivativesandFinancialInstrumentsAdditionalInformationDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#DerivativesandFinancialInstrumentsAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DerivativesandFinancialInstrumentsAdditionalInformationDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a03483-6d09-7c13-b6a8-715e006d09ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a03483-6d09-7f1f-b77c-b20e0542dceb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-7c13-b6a8-715e006d09ae" xlink:to="loc_us-gaap_DerivativeTable_01a03483-6d09-7f1f-b77c-b20e0542dceb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03483-6d09-7d01-923e-714007574796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a03483-6d09-7f1f-b77c-b20e0542dceb" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03483-6d09-7d01-923e-714007574796" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7d01-923e-714007574796_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03483-6d09-7d01-923e-714007574796" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7d01-923e-714007574796_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7a35-8600-bd13b8bba5a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03483-6d09-7d01-923e-714007574796" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7a35-8600-bd13b8bba5a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_01a03483-6d09-7e3f-83d9-0a27cfbbf7e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7a35-8600-bd13b8bba5a4" xlink:to="loc_us-gaap_ForeignExchangeContractMember_01a03483-6d09-7e3f-83d9-0a27cfbbf7e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrencySwapMember_01a03483-6d09-7a14-9e3b-accffa83f5c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CurrencySwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7a35-8600-bd13b8bba5a4" xlink:to="loc_us-gaap_CurrencySwapMember_01a03483-6d09-7a14-9e3b-accffa83f5c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_InterestRateCollarMember_01a03483-6d09-73d0-a40b-a41a12bf3e50" xlink:href="pnr-20260930.xsd#pnr_InterestRateCollarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7a35-8600-bd13b8bba5a4" xlink:to="loc_pnr_InterestRateCollarMember_01a03483-6d09-73d0-a40b-a41a12bf3e50" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_01a03483-6d09-73c0-afc9-f83353cc5324" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7a35-8600-bd13b8bba5a4" xlink:to="loc_us-gaap_InterestRateSwapMember_01a03483-6d09-73c0-afc9-f83353cc5324" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_01a03483-6d09-7b33-aa10-0a781d6703cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-7c13-b6a8-715e006d09ae" xlink:to="loc_us-gaap_DerivativeNotionalAmount_01a03483-6d09-7b33-aa10-0a781d6703cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax_01a03483-6d09-7aa4-90da-5617a7a752bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-7c13-b6a8-715e006d09ae" xlink:to="loc_us-gaap_TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax_01a03483-6d09-7aa4-90da-5617a7a752bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax_01a03483-6d09-7563-8860-421ac9343ebb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-7c13-b6a8-715e006d09ae" xlink:to="loc_us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax_01a03483-6d09-7563-8860-421ac9343ebb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ContingentEarnOutLiabilitiesFairValueDisclosure_01a03483-6d09-746a-96c2-c9f9a95e70ba" xlink:href="pnr-20260930.xsd#pnr_ContingentEarnOutLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-7c13-b6a8-715e006d09ae" xlink:to="loc_pnr_ContingentEarnOutLiabilitiesFairValueDisclosure_01a03483-6d09-746a-96c2-c9f9a95e70ba" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DerivativesandFinancialInstrumentsRecordedAmountsandEstimatedFairValuesDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#DerivativesandFinancialInstrumentsRecordedAmountsandEstimatedFairValuesDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DerivativesandFinancialInstrumentsRecordedAmountsandEstimatedFairValuesDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a03483-6d09-77ca-95e6-d2fb0f46acb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a03483-6d09-761a-94f3-1337060b6a5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-77ca-95e6-d2fb0f46acb9" xlink:to="loc_us-gaap_DerivativeTable_01a03483-6d09-761a-94f3-1337060b6a5e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_01a03483-6d09-72ac-8e1c-a49c48f5addd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a03483-6d09-761a-94f3-1337060b6a5e" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_01a03483-6d09-72ac-8e1c-a49c48f5addd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03483-6d09-72ac-8e1c-a49c48f5addd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_01a03483-6d09-72ac-8e1c-a49c48f5addd" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03483-6d09-72ac-8e1c-a49c48f5addd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a03483-6d09-7386-aa9a-18732d6e793b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_01a03483-6d09-72ac-8e1c-a49c48f5addd" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a03483-6d09-7386-aa9a-18732d6e793b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03483-6d09-71b3-a4ce-6e187083946f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a03483-6d09-7386-aa9a-18732d6e793b" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03483-6d09-71b3-a4ce-6e187083946f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_01a03483-6d09-712b-b98e-b203afab113d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03483-6d09-71b3-a4ce-6e187083946f" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_01a03483-6d09-712b-b98e-b203afab113d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a03483-6d09-7f92-8a8f-0ba93231f8c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03483-6d09-71b3-a4ce-6e187083946f" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a03483-6d09-7f92-8a8f-0ba93231f8c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtPercentageBearingVariableInterestAmount_01a03483-6d09-75d3-9c72-44f8e7b2be0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtPercentageBearingVariableInterestAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-77ca-95e6-d2fb0f46acb9" xlink:to="loc_us-gaap_LongtermDebtPercentageBearingVariableInterestAmount_01a03483-6d09-75d3-9c72-44f8e7b2be0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtPercentageBearingFixedInterestAmount_01a03483-6d09-7020-bd34-19b394e32417" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtPercentageBearingFixedInterestAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-77ca-95e6-d2fb0f46acb9" xlink:to="loc_us-gaap_LongtermDebtPercentageBearingFixedInterestAmount_01a03483-6d09-7020-bd34-19b394e32417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a03483-6d09-77a1-bb70-0afbc707fff3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a03483-6d09-77ca-95e6-d2fb0f46acb9" xlink:to="loc_us-gaap_LongTermDebt_01a03483-6d09-77a1-bb70-0afbc707fff3" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/DerivativesandFinancialInstrumentsAssetsandLiabilitiesMeasuredatFairValueDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#DerivativesandFinancialInstrumentsAssetsandLiabilitiesMeasuredatFairValueDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/DerivativesandFinancialInstrumentsAssetsandLiabilitiesMeasuredatFairValueDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03483-6d09-7ed5-966f-26678d069529" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03483-6d09-7ed5-966f-26678d069529" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a03483-6d09-7ae5-a183-6073ec6187f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03483-6d09-7ed5-966f-26678d069529" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a03483-6d09-7ae5-a183-6073ec6187f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03483-6d09-7ae5-a183-6073ec6187f7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a03483-6d09-7ae5-a183-6073ec6187f7" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03483-6d09-7ae5-a183-6073ec6187f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03483-6d09-7ee2-8a93-02dd28bb3c00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a03483-6d09-7ae5-a183-6073ec6187f7" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03483-6d09-7ee2-8a93-02dd28bb3c00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_01a03483-6d09-755b-a182-afc328566e60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03483-6d09-7ee2-8a93-02dd28bb3c00" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_01a03483-6d09-755b-a182-afc328566e60" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_01a03483-6d09-79fb-95af-88a506729700" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03483-6d09-7ee2-8a93-02dd28bb3c00" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_01a03483-6d09-79fb-95af-88a506729700" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_01a03483-6d09-736d-80f3-3a895c6115d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03483-6d09-7ee2-8a93-02dd28bb3c00" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_01a03483-6d09-736d-80f3-3a895c6115d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_01a03483-6d09-7bbc-a9a0-7c4a7d49ddf9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03483-6d09-7ed5-966f-26678d069529" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_01a03483-6d09-7bbc-a9a0-7c4a7d49ddf9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_01a03483-6d09-7bbc-a9a0-7c4a7d49ddf9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_01a03483-6d09-7bbc-a9a0-7c4a7d49ddf9" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_01a03483-6d09-7bbc-a9a0-7c4a7d49ddf9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_01a03483-6d09-7b21-afad-4dbdfe35ba40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_01a03483-6d09-7bbc-a9a0-7c4a7d49ddf9" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_01a03483-6d09-7b21-afad-4dbdfe35ba40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_01a03483-6d09-7238-8391-7989c5797f6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_01a03483-6d09-7b21-afad-4dbdfe35ba40" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_01a03483-6d09-7238-8391-7989c5797f6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03483-6d09-7db2-be13-a5c7dfac3357" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03483-6d09-7ed5-966f-26678d069529" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03483-6d09-7db2-be13-a5c7dfac3357" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7db2-be13-a5c7dfac3357_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03483-6d09-7db2-be13-a5c7dfac3357" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7db2-be13-a5c7dfac3357_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7954-a389-4d84c328cb17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03483-6d09-7db2-be13-a5c7dfac3357" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7954-a389-4d84c328cb17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_01a03483-6d09-7029-94fc-7416d1d56614" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a03483-6d09-7954-a389-4d84c328cb17" xlink:to="loc_us-gaap_InterestRateContractMember_01a03483-6d09-7029-94fc-7416d1d56614" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_01a03483-6d09-7507-9337-2d50407e6fde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_us-gaap_DerivativeAssets_01a03483-6d09-7507-9337-2d50407e6fde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_01a03483-6d09-788a-b054-aa009d48735b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_us-gaap_DerivativeLiabilities_01a03483-6d09-788a-b054-aa009d48735b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_01a03483-6d09-709b-bd9f-71b1ebdcca35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyContractAssetFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_01a03483-6d09-709b-bd9f-71b1ebdcca35" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_01a03483-6d09-758d-bc59-12d006a001f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_us-gaap_ForeignCurrencyContractsLiabilityFairValueDisclosure_01a03483-6d09-758d-bc59-12d006a001f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DeferredCompensationPlanAssetsFairValueDisclosure_01a03483-6d09-7d61-aa0a-098d91f9b313" xlink:href="pnr-20260930.xsd#pnr_DeferredCompensationPlanAssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_pnr_DeferredCompensationPlanAssetsFairValueDisclosure_01a03483-6d09-7d61-aa0a-098d91f9b313" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_ContingentEarnOutLiabilitiesFairValueDisclosure_01a03483-6d09-7886-806b-92bc1e305706" xlink:href="pnr-20260930.xsd#pnr_ContingentEarnOutLiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_pnr_ContingentEarnOutLiabilitiesFairValueDisclosure_01a03483-6d09-7886-806b-92bc1e305706" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet_01a03483-6d09-77a1-abaa-325b27ec30a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet_01a03483-6d09-77a1-abaa-325b27ec30a9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill_01a03483-6d09-7bf6-a4b6-1cc98636a81e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03483-6d09-7a64-a1af-c88fdb3e439d" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill_01a03483-6d09-7bf6-a4b6-1cc98636a81e" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/ShareholdersEquityDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#ShareholdersEquityDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/ShareholdersEquityDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:href="pnr-20260930.xsd#pnr_StockholdersEquityNoteDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_StockholdersEquityNoteDisclosureTable_01a03483-6d09-785e-a7bb-1b512ebda863" xlink:href="pnr-20260930.xsd#pnr_StockholdersEquityNoteDisclosureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:to="loc_pnr_StockholdersEquityNoteDisclosureTable_01a03483-6d09-785e-a7bb-1b512ebda863" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_01a03483-6d09-7681-a300-fd7d86d2d4ad" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureTable_01a03483-6d09-785e-a7bb-1b512ebda863" xlink:to="loc_srt_ShareRepurchaseProgramAxis_01a03483-6d09-7681-a300-fd7d86d2d4ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_01a03483-6d09-7681-a300-fd7d86d2d4ad_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_01a03483-6d09-7681-a300-fd7d86d2d4ad" xlink:to="loc_srt_ShareRepurchaseProgramDomain_01a03483-6d09-7681-a300-fd7d86d2d4ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_01a03483-6d09-7822-98fd-b950c3d02dbb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_01a03483-6d09-7681-a300-fd7d86d2d4ad" xlink:to="loc_srt_ShareRepurchaseProgramDomain_01a03483-6d09-7822-98fd-b950c3d02dbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_December2025ShareRepurchaseProgramMember_01a03483-6d09-717b-8ae6-e9601052db13" xlink:href="pnr-20260930.xsd#pnr_December2025ShareRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_01a03483-6d09-7822-98fd-b950c3d02dbb" xlink:to="loc_pnr_December2025ShareRepurchaseProgramMember_01a03483-6d09-717b-8ae6-e9601052db13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_01a03483-6d09-77a6-9718-f25d5fe41b1d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_01a03483-6d09-77a6-9718-f25d5fe41b1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a03483-6d09-76dc-b707-87a207ecaedd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a03483-6d09-76dc-b707-87a207ecaedd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a03483-6d09-75f1-9552-7ad34681f282" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a03483-6d09-75f1-9552-7ad34681f282" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_01a03483-6d09-7b18-bc86-61002d43155a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_01a03483-6d09-7b18-bc86-61002d43155a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_01a03483-6d09-7194-911f-8fa64a062e20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_01a03483-6d09-7194-911f-8fa64a062e20" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrent_01a03483-6d09-7390-b4c6-511c0dcf3b9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:to="loc_us-gaap_DividendsPayableCurrent_01a03483-6d09-7390-b4c6-511c0dcf3b9b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramExpirationDate_01a03483-6d09-78c3-9610-421d8842ed67" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramExpirationDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pnr_StockholdersEquityNoteDisclosureLineItems_01a03483-6d09-7af9-b760-4932cd778e04" xlink:to="loc_srt_StockRepurchaseProgramExpirationDate_01a03483-6d09-78c3-9610-421d8842ed67" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SegmentInformationFinancialInformationByReportableSegmentDetail" xlink:type="simple" xlink:href="pnr-20260930.xsd#SegmentInformationFinancialInformationByReportableSegmentDetail"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SegmentInformationFinancialInformationByReportableSegmentDetail" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-726d-904a-ecb3d32e456f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03483-6d09-7dc5-b583-e25e347f0dbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-726d-904a-ecb3d32e456f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03483-6d09-7dc5-b583-e25e347f0dbc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-734b-8003-792c922f2591" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03483-6d09-7dc5-b583-e25e347f0dbc" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-734b-8003-792c922f2591" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03483-6d09-734b-8003-792c922f2591_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-734b-8003-792c922f2591" xlink:to="loc_us-gaap_SegmentDomain_01a03483-6d09-734b-8003-792c922f2591_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03483-6d09-7157-955b-f05869a5decb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d09-734b-8003-792c922f2591" xlink:to="loc_us-gaap_SegmentDomain_01a03483-6d09-7157-955b-f05869a5decb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_FlowMember_01a03483-6d09-76d6-963f-a1c5d54eae45" xlink:href="pnr-20260930.xsd#pnr_FlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-7157-955b-f05869a5decb" xlink:to="loc_pnr_FlowMember_01a03483-6d09-76d6-963f-a1c5d54eae45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WaterSolutionsMember_01a03483-6d09-73b1-8e8c-ed532a590aba" xlink:href="pnr-20260930.xsd#pnr_WaterSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-7157-955b-f05869a5decb" xlink:to="loc_pnr_WaterSolutionsMember_01a03483-6d09-73b1-8e8c-ed532a590aba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PoolMember_01a03483-6d09-76c5-95e8-22925a032559" xlink:href="pnr-20260930.xsd#pnr_PoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d09-7157-955b-f05869a5decb" xlink:to="loc_pnr_PoolMember_01a03483-6d09-76c5-95e8-22925a032559" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a03483-6d09-742d-a2b4-17a0207e8169" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03483-6d09-7dc5-b583-e25e347f0dbc" xlink:to="loc_srt_ConsolidationItemsAxis_01a03483-6d09-742d-a2b4-17a0207e8169" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a03483-6d09-742d-a2b4-17a0207e8169_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_01a03483-6d09-742d-a2b4-17a0207e8169" xlink:to="loc_srt_ConsolidationItemsDomain_01a03483-6d09-742d-a2b4-17a0207e8169_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a03483-6d09-7086-8e63-be4b43029229" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_01a03483-6d09-742d-a2b4-17a0207e8169" xlink:to="loc_srt_ConsolidationItemsDomain_01a03483-6d09-7086-8e63-be4b43029229" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_01a03483-6d0a-7248-a428-43be88c90b31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a03483-6d09-7086-8e63-be4b43029229" xlink:to="loc_us-gaap_OperatingSegmentsMember_01a03483-6d0a-7248-a428-43be88c90b31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_01a03483-6d0a-71bd-a147-e1b8a9004ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a03483-6d09-7086-8e63-be4b43029229" xlink:to="loc_us-gaap_CorporateNonSegmentMember_01a03483-6d0a-71bd-a147-e1b8a9004ec8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a03483-6d0a-7898-b5aa-f6a6acd264cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-726d-904a-ecb3d32e456f" xlink:to="loc_us-gaap_Assets_01a03483-6d0a-7898-b5aa-f6a6acd264cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_01a03483-6d0a-7e55-9648-d6fea1e1860d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-726d-904a-ecb3d32e456f" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_01a03483-6d0a-7e55-9648-d6fea1e1860d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_01a03483-6d0a-7357-bc38-93355ca28d0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-726d-904a-ecb3d32e456f" xlink:to="loc_us-gaap_Depreciation_01a03483-6d0a-7357-bc38-93355ca28d0d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pentair.com/role/SegmentInformationReconciliationofIncomefromContinuingOperationsfromSegmentstoConsolidatedDetails" xlink:type="simple" xlink:href="pnr-20260930.xsd#SegmentInformationReconciliationofIncomefromContinuingOperationsfromSegmentstoConsolidatedDetails"/>
  <link:definitionLink xlink:role="http://www.pentair.com/role/SegmentInformationReconciliationofIncomefromContinuingOperationsfromSegmentstoConsolidatedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03483-6d0a-72c9-affc-224e86d05bd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03483-6d0a-72c9-affc-224e86d05bd2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a03483-6d0a-7954-aaca-7771b4087aaa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03483-6d0a-72c9-affc-224e86d05bd2" xlink:to="loc_srt_ConsolidationItemsAxis_01a03483-6d0a-7954-aaca-7771b4087aaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a03483-6d0a-7954-aaca-7771b4087aaa_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_01a03483-6d0a-7954-aaca-7771b4087aaa" xlink:to="loc_srt_ConsolidationItemsDomain_01a03483-6d0a-7954-aaca-7771b4087aaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a03483-6d0a-755b-81c6-fa483ac86771" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_01a03483-6d0a-7954-aaca-7771b4087aaa" xlink:to="loc_srt_ConsolidationItemsDomain_01a03483-6d0a-755b-81c6-fa483ac86771" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_01a03483-6d0a-754c-96e8-02d4b139fa14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a03483-6d0a-755b-81c6-fa483ac86771" xlink:to="loc_us-gaap_OperatingSegmentsMember_01a03483-6d0a-754c-96e8-02d4b139fa14" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_01a03483-6d0a-7012-ae14-b56a0d85c5d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a03483-6d0a-755b-81c6-fa483ac86771" xlink:to="loc_us-gaap_CorporateNonSegmentMember_01a03483-6d0a-7012-ae14-b56a0d85c5d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_01a03483-6d0a-73ec-8a13-92745bc9507e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a03483-6d0a-755b-81c6-fa483ac86771" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_01a03483-6d0a-73ec-8a13-92745bc9507e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d0a-7177-bf90-ba7fd1ab678e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03483-6d0a-72c9-affc-224e86d05bd2" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d0a-7177-bf90-ba7fd1ab678e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03483-6d0a-7177-bf90-ba7fd1ab678e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d0a-7177-bf90-ba7fd1ab678e" xlink:to="loc_us-gaap_SegmentDomain_01a03483-6d0a-7177-bf90-ba7fd1ab678e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03483-6d0a-73ae-84de-2c42bf7f37f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03483-6d0a-7177-bf90-ba7fd1ab678e" xlink:to="loc_us-gaap_SegmentDomain_01a03483-6d0a-73ae-84de-2c42bf7f37f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_FlowMember_01a03483-6d0a-77e8-b21f-30479d37f89a" xlink:href="pnr-20260930.xsd#pnr_FlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d0a-73ae-84de-2c42bf7f37f3" xlink:to="loc_pnr_FlowMember_01a03483-6d0a-77e8-b21f-30479d37f89a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_WaterSolutionsMember_01a03483-6d0a-752d-b070-025923657d88" xlink:href="pnr-20260930.xsd#pnr_WaterSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d0a-73ae-84de-2c42bf7f37f3" xlink:to="loc_pnr_WaterSolutionsMember_01a03483-6d0a-752d-b070-025923657d88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_PoolMember_01a03483-6d0a-7e6a-ae04-1c57a647621c" xlink:href="pnr-20260930.xsd#pnr_PoolMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03483-6d0a-73ae-84de-2c42bf7f37f3" xlink:to="loc_pnr_PoolMember_01a03483-6d0a-7e6a-ae04-1c57a647621c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a03483-6d0a-74ea-842d-bdbc75730016" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a03483-6d0a-74ea-842d-bdbc75730016" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_01a03483-6d0a-7561-b3ab-cace5d424166" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_01a03483-6d0a-7561-b3ab-cace5d424166" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_01a03483-6d0a-7d70-ae0b-df02c7a72dae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_OperatingExpenses_01a03483-6d0a-7d70-ae0b-df02c7a72dae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a03483-6d0a-7d24-a5ba-4200e5fd70f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a03483-6d0a-7d24-a5ba-4200e5fd70f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_01a03483-6d0a-7ef7-aa64-a1f2e78226be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_RestructuringCharges_01a03483-6d0a-7ef7-aa64-a1f2e78226be" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_TransformationCosts_01a03483-6d0a-7987-9284-ef7bd8625458" xlink:href="pnr-20260930.xsd#pnr_TransformationCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_pnr_TransformationCosts_01a03483-6d0a-7987-9284-ef7bd8625458" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_01a03483-6d0a-7a43-8c1f-66d732d7e681" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_AssetImpairmentCharges_01a03483-6d0a-7a43-8c1f-66d732d7e681" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_01a03483-6dba-7714-9e89-121ab0341a81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_01a03483-6dba-7714-9e89-121ab0341a81" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pnr_DealRelatedExpenses_01a159e2-2578-79b3-9061-904a76000e8c" xlink:href="pnr-20260930.xsd#pnr_DealRelatedExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_pnr_DealRelatedExpenses_01a159e2-2578-79b3-9061-904a76000e8c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_01a03483-6dba-7f38-aa16-ceaa6f693d89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_01a03483-6dba-7f38-aa16-ceaa6f693d89" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRevenueExpenseNet_01a03483-6dba-7867-aa5c-3d4483e37e7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRevenueExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_InterestRevenueExpenseNet_01a03483-6dba-7867-aa5c-3d4483e37e7d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_01a03483-6dba-720c-84a8-9c3262a8f676" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_OtherExpenses_01a03483-6dba-720c-84a8-9c3262a8f676" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a03483-6dba-785e-b715-f41a0b147278" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03483-6d0a-7a00-b62d-583b9be3685f" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a03483-6dba-785e-b715-f41a0b147278" xlink:type="arc" order="12"/>
  </link:definitionLink>
</link:linkbase>
