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information to the Commission pursuant to Rule 12g3-2(b) under
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Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Quarterly Financial Information for

the period ended March 31, 2026

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statements of Financial Position as of March 31, 2026 and December 31, 2025 In thousands of reais

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statements of Financial Position as of March 31, 2026 and December 31, 2025 In thousands of reais

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statements of Financial Position as of March 31, 2026 and December 31, 2025 In thousands of reais

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statements of Income for the Periods ended March 31, 2026 and 2025 In thousands of reais, unless otherwise stated

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statements of Comprehensive Income for the Periods ended March 31, 2026 and 2025 In thousands of reais, unless otherwise stated

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statement of Changes in Equity for the Periods ended March 31, 2026 and 2025 In thousands of reais, unless otherwise stated

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statements of Cash Flows for the Periods ended March 31, 2026 and 2025 In thousands of reais, unless otherwise stated

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statements of Cash Flows for the Periods ended March 31, 2026 and 2025 In thousands of reais, unless otherwise stated

Companhia de Saneamento Básico do Estado de São Paulo - SABESP   Statements of Value Added for the Periods ended March 31, 2026 and 2025 In thousands of reais

May 7, 2026

SÃO PAULO, SP – Sabesp (SBSP3) reported adjusted earnings of R$0.44 per share in the 1Q26, compared to R$0.34 per share in the same period of the previous year.

“We entered 2026 maintaining strong execution momentum. In 1Q26, investments totaled R$3.7 billion, a 31% increase versus 1Q25, supporting operational expansion and service quality improvements. Adjusted EBITDA reached R$3.8 billion (+26% y/y) and Adjusted Net Income¹ totaled R$1.6 billion (+32% y/y), reinforcing the consistency of our operating performance and financial discipline,” said Daniel Szlak, CFO of Sabesp.

“Beyond the financial results, our priority continues to be delivering tangible advances in sanitation coverage and service standards. We are consistently outperforming the U-Factor benchmarks for the 2024–2026 cycle, with targets at 87% in water supply, 77% in sewage collection, and 71% in sewage treatment, reflecting sustained operational improvements rather than one-off gains.

Our investment program is driving broad social and economic impact by expanding access to essential services while strengthening communities through large-scale infrastructure execution, positioning the Company to sustain and scale these outcomes throughout 2026,” said Carlos Piani, CEO of Sabesp.

Consolidated Results

For the quarter ended March 31, 2026, Sabesp reported adjusted earnings per share³ of R$0.44 compared to R$0.34 recorded in the same period of the previous year. Performance was driven by volume growth resulting from new connections (U-Factor targets fully attained), tariff gains and better collection, partially offset by the change in customer mix, with the expansion of consumers with access to subsidized rates².

The quarter sustained strong efficiency gains, driven by reductions in general and administrative expenses, headcount reduction, power optimization with shifts to the free market, and better collection rates. As a result, Adjusted EBITDA increased by 26%, reaching R$3.8 billion in 1Q26, while Adjusted Net Income grew by 32%, totaling R$1.6 billion

Sabesp invested R$3.7 bn in 1Q26, a 31% increase over the same period of the previous year, focusing on expansion projects directly aimed at meeting universalization targets.

Earnings Conference Call

Will be held on May 8, 2026, at 10:00 AM (Brasília time). Access link is available at the Company’s Investor Relations website. The presentation has been made available at the same website. An audio recording of the call will be posted at the same website.

REPORTED INCOME STATEMENT (CONSOLIDATED)

R$ mn

ADJUSTED INCOME STATEMENT (CONSOLIDATED)

1Q26

R$ mn

*Balance adjusted by construction revenue/cost

Non-recurring effects on 1Q26 EBITDA: R$ (16) mn related to M&A expenses.

Due to the migration to SAP S/4HANA, a temporary cutover reduced March 2026 billing by two days. This effect negatively impacted billing volumes and revenues in the period and is expected to be recovered over the subsequent months.

In 1Q26, total water production reached 778 million cubic meters, 4.6% lower year-over-year compared to 1Q25. This decline reflects a milder summer, with average temperatures 3.3 °C lower than last year, as well as the application of SP Aguas operational rule of the night pressure management implemented for approximately 10 hours per day to enhance the system resilience.

ADJUSTED NET REVENUE

Adjusted net revenue from sanitation services, considering FAUSP and taxes, totaled R$ 6,021 mn in 1Q26, an increase of +10.9% vs 1Q25. The main factors that impacted revenue in the period were:

CONSUMPTION BY CATEGORY

Wholesale and Others in 1Q25 was adjusted to incorporate the amount related to Olímpia.

(1) Active and registered connections, average at the end of the period

Not audited by external auditors

COST AND EXPENSE

In 1Q26, OPEX decreased by 7.7% compared to 1Q25, representing a reduction of R$ 188 mn. This performance was mainly driven by: (i) R$ 170 mn in savings in personnel expenses, reflecting an 13% headcount reduction, workforce mix and labor benefits streamlining; (ii) energy cost savings, primarily due to the migration from the regulated market to the free market, reaching 86% (+12.6pp y/y). These effects were partially offset by higher general expenses related to municipal funds (FMSAI), reflecting higher revenues compared to last year.

R$ mn

PERSONNEL

Sabesp ended 1Q26 with 8,927 employees, 8% reduction vs the same period of the previous year, and a 13% reduction

when considering the average number of employees.

CAPITAL EXPENDITURSES

In 1Q26, CapEx totaled R$ 3,728 mn, an increase of 30.8% compared to the same period of the previous year.

R$ mn

BALANCE SHEET (CONSOLIDATED)

STATEMENT OF CASH FLOWS (CONSOLIDATED)

Companhia de Saneamento Básico do Estado de São Paulo – SABESP   Notes to the Financial Statements for the Period ended March 31, 2026 In thousands of reais, unless otherwise stated

Companhia de Saneamento Básico do Estado de São Paulo (“SABESP”) is a publicly-held corporation headquartered in the municipality of São Paulo, at Rua Costa Carvalho, 300, CEP 05429-900. SABESP and its direct and indirect subsidiaries, individually or collectively (the “Company”), is engaged in the provision of basic and environmental sanitation services in São Paulo State, and supplies treated water and sewage services on a wholesale basis. SABESP may perform activities in other states and countries and can operate in drainage, urban cleaning, solid waste handling, and energy markets.

Since January 2026, following the acquisition of Empresa Metropolitana de Águas e Energia (“EMAE”), the Company has also begun operating in the planning, construction, operation, and maintenance of energy generation systems, as well as in the commercialization of electric power.

The Company's shares have been listed on the Novo Mercado segment of B3 under ticker SBSP3 since April 2002 and on the New York Stock Exchange (“NYSE”) as Level III American Depositary Receipts (“ADRs”), under ticker SBS, since May 2002.

Approvals

The quarterly financial information was approved by the Board of Directors on May 7, 2026.

2                 Basis of preparation and presentation of the quarterly information

The quarterly information as of March 31 ,2026, was prepared based on the provisions of CPC 21 (R1) – Interim Financial Statements and the international standard IAS 34 – Interim Financial Reporting, issued by the International Accounting Standards Board (IASB), applicable to the preparation of Quarterly Information (ITR), and presented according to the rules issued by the CVM. Accordingly, this quarterly information takes into consideration the Circular Letter CVM/SNC/SEP 003 of April 28, 2011, which allows the entities to present selected notes to the financial statements in cases of redundant information already disclosed in the Annual Financial Statements. The quarterly information as of March 31, 2026, shall be read jointly with the Annual Financial Statements as of December 31, 2025, issued on March 16, 2026, prepared under the International Financial Reporting Standards (IFRS), issued by the International Accounting Standards Board (IASB), and the accounting practices adopted in Brazil, which observe the pronouncements issued by the Brazilian Accounting Pronouncements Committee (CPC). Therefore, the explanatory notes of this quarterly information are not presented or are not at the same level of detail and/or with the same reference as the notes included in the Annual Financial Statements (according to numerical references):

All material information related to the quarterly information, and this information alone, is being disclosed and corresponds to the information used by the Company’s Management in its administration.

The Company prepared the financial statements on a going concern basis.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP   Notes to the Financial Statements for the Period ended March 31, 2026 In thousands of reais, unless otherwise stated

The amounts disclosed in the Notes are presented in thousands of reais, unless otherwise stated.

3                 Summary of material accounting policy information

The material accounting policy information used in the preparation of the quarterly information as of March 31, 2026, is consistent with that used to prepare the Annual Financial Statements for the year ended December 31, 2025. As a result of the business combination completed in the current quarter (Note 4), the following accounting policies have become applicable to the Company:

Business combination

Business combinations are accounted for using the acquisition method. The cost of an acquisition is measured by the sum of the consideration paid, which is evaluated based on the fair value on the acquisition date, and the value of any non-controlling interests in the acquiree. For each business combination, the acquirer must measure the non-controlling interest in the acquiree at fair value or based on its interest in the net assets identified in the acquiree. Costs directly attributable to the acquisition are accounted for as expense when incurred.

The Company determines that it has acquired a business when the acquired set of activities and assets includes, at least, an input of resources and a substantive process that together contribute significantly to the ability to generate output of resources. The process acquired is considered substantive if it is essential to the ability to develop or convert the input of resources acquired into outputs of resources (and the inputs of resources acquired include both the organized workforce with the skills, knowledge or experience necessary to perform this process); or is critical to the ability to continue producing outputs and is considered unique or scarce, or cannot be replaced without significant cost, effort or delay in the ability to continue producing outputs of resources.

Any contingent consideration to be paid by the acquirer will be recognized at fair value on the acquisition date. Subsequent changes in the fair value of the contingent consideration deemed as an asset or as a liability shall be recognized in accordance with CPC 48 / IFRS 9 in the profit or loss statement.

Initially, goodwill is measured as the excess of the consideration paid in relation to the net assets acquired (identifiable assets acquired, net, and liabilities assumed). If the consideration is less than the fair value of the net assets acquired, the difference shall be recognized as gain in the profit or loss statement.

After initial recognition, goodwill is measured at cost, less any accumulated impairment losses. For impairment testing purposes, the goodwill acquired in a business combination is, as of the acquisition date, allocated to each of the Company's cash-generating units that are expected to benefit from the synergies of the combination, regardless of whether other assets or liabilities of the acquiree are attributed to those units.

When a goodwill is part of a cash-generating unit and a portion of that unit is disposed of, the goodwill associated with the portion disposed of must be included in the cost of the operation when determining the gain or loss on disposal. The goodwill disposed of in these circumstances is calculated based on the proportional values of the portion disposed of in relation to the cash-generating unit held.

4                 Business combination and acquisition of non-controlling interests

Empresa Metropolitana de Águas e Energia S.A. (“EMAE”)

On January 21, 2026, the Company acquired 29.9% of the total capital and 74.9% of the voting capital of EMAE, representing 11,009,550 (eleven million, nine thousand, five hundred and fifty) common shares of the company that focuses on the planning, construction, operation and maintenance of electricity generation systems, as well as their commercialization, operating under a concession regime. The transaction was motivated by a combination of factors:

Companhia de Saneamento Básico do Estado de São Paulo – SABESP   Notes to the Financial Statements for the Period ended March 31, 2026 In thousands of reais, unless otherwise stated

This holistic approach reflects SABESP's strategy to strengthen its position as an essential services company in a context of climate challenges, growing demand and the need for better operational efficiency.

Assets acquired and liabilities assumed

In accordance with the provisions of CPC 15/IFRS 3, although the acquisition of control and, consequently, the business combination occurred on January 21, 2026, the Company considered the beginning of the acquisition month, i.e., January 1, 2026, for purposes of measuring the acquired assets and assumed liabilities, the Company adopted the beginning of the acquisition month, January 1, 2026, as the effective acquisition date, applying a three-month reporting lag as permitted by the applicable accounting standards. Based on this date, no results of the acquire are included in the consolidated financial statements. The fair value of EMAE’s identifiable assets and liabilities as of that date is presented below:

These effects are preliminary, as at the date of this disclosure the procedures for the purchase price allocation are still in progress, primarily related to the inspection of the acquired fixed assets, among other analyses. The final allocation of EMAE’s purchase price depends on valuations and other studies that have not yet been completed, as well as on the issuance of the final appraisal report to be prepared by an independent specialized firm.

The goodwill/identifiable asset amounting to R$ 504,910 recognized upon the acquisition arises substantially from expected synergies associated with the business combination. This amount is provisional and subject to the completion of the

Companhia de Saneamento Básico do Estado de São Paulo – SABESP   Notes to the Financial Statements for the Period ended March 31, 2026 In thousands of reais, unless otherwise stated

purchase price allocation (PPA) process, and may be adjusted as the fair value assessments of the identifiable assets acquired and liabilities assumed are finalized.

The Company adopted, as an accounting policy, the measurement and initial recognition of the non-controlling interest using the proportional interest share method.

The total consideration given was settled exclusively in cash, so that there are no clauses providing for supplementary payment by means of contingent payment, put/call option, issue or transfer of shares, assumption of liabilities or transfer of other assets to acquire the interest.

The disclosure of pro forma net operating revenue and net income was not presented, as the acquisition balance sheet already reflects the effects as of the beginning of the fiscal year.

Transaction costs in the amount of R$ 16,000 were recognized in the profit or loss statement as general and administrative expenses.

Acquisition of additional interest in EMAE

After obtaining control, the Company acquired additional non-controlling interests, increasing its shareholding to 79.31%:

The carrying amount of the net assets as of the acquisition date amounted to R$ 294,021. The breakdown of the additional interest acquired is shown below:

5                 Risk management

5.1            Financial risk management

Financial risk factors

The Company's activities are affected by the Brazilian economic scenario, making it exposed to market risk (exchange rate and interest rate), credit risk, and liquidity risk. Financial risk management focuses on the unpredictability of financial markets and seeks to minimize potential adverse effects on financial performance. There were no changes in risk measurement policies, processes, and methods compared to the previous year.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP   Notes to the Financial Statements for the Period ended March 31, 2026 In thousands of reais, unless otherwise stated

(a)            Market risk

Foreign currency risk

It is the risk that the fair value of the future cash flows of a financial instrument will fluctuate due to variations in exchange rates. The Company's exposure to the risk of changes in exchange rates refers mainly to its financing activities, since the Company has foreign currency-denominated liabilities arising from long-term financing, in development institutions in US Dollar, Euro and Yen.

The management of currency exposure considers several current and projected economic factors, besides market conditions.

This risk arises from the possibility that the Company may incur losses due to exchange rate fluctuations that would impact liability balances of foreign currency-denominated borrowings and financing and related finance costs. The Company manages its foreign exchange risk through hedging transactions since 2024 and negotiates the terms of the derivatives in order to comply with the terms of the exposure hedged under Note 19.

Part of the total financial debt in the amount of R$ 17,879,630 as of March 31, 2026 (R$ 10,632,252 as of December 31, 2025), is indexed to the U.S. dollar, Euro and Yen. The exposure to currency risk is as follows:

Companhia de Saneamento Básico do Estado de São Paulo – SABESP   Notes to the Financial Statements for the Period ended March 31, 2026 In thousands of reais, unless otherwise stated

The table below shows the prices and exchange rate changes in the period: