Indicate by check mark whether the registrant by furnishing the
information contained in this Form is also thereby furnishing the
information to the Commission pursuant to Rule 12g3-2(b) under
the Securities Exchange Act of 1934.

Yes ______ No ___X___

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Financial Statements as of

December 31, 2025 and 2024 

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Table of Contents of the 2025 Financial Statements

A free translation from Portuguese into English of Independent Auditor’s Report on financial statements prepared in Brazilian currency in accordance with the accounting practices adopted in Brazil and the International Financial Reporting Standards (IFRS) issued by the International Accounting Standards Board (IASB)

Independent auditor’s report on individual and consolidated financial statements

The Shareholders, Board of Directors and Officers

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Opinion

We have audited the individual and consolidated financial statements of Companhia de Saneamento Básico do Estado de São Paulo - SABESP (the “Company”), identified as individual and consolidated, respectively, which comprise the statement of financial position as at December 31, 2025 and the statements of income, of comprehensive income, of changes in equity, and of cash flows for the year then ended, and the notes to the financial statements, including material accounting policies and other explanatory information.

In our opinion, the accompanying individual and consolidated financial statements present fairly, in all material respects, the Company’s individual and consolidated financial position as at December 31, 2025, its individual and consolidated financial performance and its individual and consolidated cash flows for the year then ended, in accordance with the accounting practices adopted in Brazil and the International Financial Reporting Standards (IFRS) issued by the International Accounting Standards Board (IASB).

Basis for opinion

We conducted our audit in accordance with the Brazilian and International Standards on Auditing. Our responsibilities under those standards are further described in the “Auditor’s responsibilities for the audit of the individual and consolidated financial statements” section of our report. We are independent of the Company and its subsidiaries in accordance with the relevant ethical principles set forth in the Code of Professional Ethics for Accountants and the professional standards issued by Brazil’s National Association of State Boards of Accountancy (CFC), applicable to audits of financial statements in Brazil, and we have fulfilled our other ethical responsibilities in accordance with these requirements. We believe that the audit evidence we have obtained is sufficient and appropriate to provide a basis for our opinion.

Key audit matters

Key audit matters are those matters that, in our professional judgment, were of most significance in our audit of the financial statements of the current year. These matters were addressed in the context of our audit of the individual and consolidated financial statements as a whole, and in forming our opinion thereon, and we do not provide a separate opinion on these matters. For each matter below, a description of how our audit addressed the matter, including any commentary on the findings or outcome of our procedures, is provided in the context of the financial statements taken as a whole.

We have fulfilled the responsibilities described in the “Auditor’s responsibilities for the audit of the individual and consolidated financial statements” section of our report, including in relation to these key audit matters. Accordingly, our audit included the performance of procedures designed to respond to our assessment of the risks of material misstatement of the financial statements. The results of our audit procedures, including the procedures performed to address the matters below, provide the basis for our audit opinion on the accompanying financial statements.

Contract Asset Related to Service Concession Agreements

As mentioned in Note 13 to the individual and consolidated financial statements, in the year ended December 31, 2025, the Contract Asset related to service concession agreements is recognized at fair value during the construction period. This Contract Asset represent the right to consideration in exchange for goods or services transferred to the customer under the existing service concession agreements. The expenditures incurred on the infrastructure serving the concession are an essential component of the methodology applied by the granting authority for determining the tariff to be charged to end consumers and the indemnification to be received by the Company upon termination of the service concession agreements. As disclosed in Note 13 (i), additions to Contract Assets for the year amounted to R$14,430,593 thousand in the individual financial statements and R$14,437,363 thousand in the consolidated financial statements.

These transactions recognized in Contract Assets involve material amounts, are decentralized across various municipalities/projects, involve high transaction volumes, and require judgment in determining which expenditures qualify as investments in concession infrastructure that will be eligible for capitalization. Therefore, we considered this to be a key audit matter.

How our audit addressed this matter

Our audit procedures on concession-related Contract Assets included, among others, analyzing the nature of expenditures incurred in the construction of infrastructure during the year, analyzing their adherence to the terms of the existing service concession agreements and the applicable accounting standards; reviewing the supplier base and selecting samples for detailed testing of suppliers with the highest transaction volumes (by value or recurrence) during the year, applying unpredictability criteria to our sampling; evaluating the competence and reputation of key suppliers through media research, restrictive lists, and registration status; conducting field inspections of ongoing construction works, selected based on relevance and unpredictability criteria, to verify the existence of assets/infrastructure under construction; obtaining external confirmations from suppliers with the highest transaction volumes during the year (by value or recurrence); performing tests on journal entries, reviewing debits in the contract asset account against matching entries that were inconsistent with the nature of the transaction; and assessing the adequacy of the disclosures in the corresponding notes to the individual and consolidated financial statements as at December 31, 2025.

Based on the outcome of our audit procedures performed on the Contract Assets related to the service concession agreements, which are consistent with the executive board’s assessment, we consider that the criteria and assumptions adopted by the executive board, as well as the respective disclosures in Note 13, are acceptable in the context of the financial statements taken as a whole.

Revenue from sanitation services

As mentioned in Note 30 to the individual and consolidated financial statements, in the year ended December 31, 2025, revenue from the provision of water supply and sewage services, which comprises individual and consolidated net operating revenue, are recognized based on water consumption or on the rendering of services, it also includes unbilled revenue, which represents revenue incurred for services rendered but not billed by year-end, and are recognized based on estimates. These revenues involve highly dispersed and high-volume transactions, and in addition, measuring unbilled revenue involves the executive board’s judgment, considering the estimates required to identify and measure the volume of water supply and sewage services provided but not billed at year-end. Therefore, we considered this to be a key audit matter. 

How our audit addressed this matter

Our audit procedures on revenue from sanitation services included, among others, performing correlation tests on journal entries among revenue, accounts receivable, and cash accounts; carrying out anchor testing on cash inflows utilized to settle accounts receivable; performing cut-off procedures, including reviewing transactions close to year end; analyzing changes in revenue, accounts receivable, and cash through substantive analytical procedures; testing debt balances recorded in revenue accounts, analyzing any transactions lacking matching entries consistent with the nature of the Company’s operations and business; performing substantive analytical procedures on unbilled revenue and recalculating a sample of invoices; as well as assessing the adequacy of the disclosures in the corresponding notes to the individual and consolidated financial statements as at December 31, 2025.

Based on the outcome of our audit procedures on revenue from sanitation services, which is consistent with the executive board’s assessment, we consider that the criteria and estimates adopted by the executive board, as well as the respective disclosures in Note 30 are acceptable in the context of the financial statements taken as a whole.

Other matters

Audit of corresponding figures

The Company’s financial statements for the year ended December 31, 2024 were audited by another independent auditor, who issued an unmodified audit report dated March 24, 2025.

Statements of value added

The individual and consolidated statements of value added (SVA) for the year ended December 31, 2025, prepared under the responsibility of Company’s executive board, and presented as supplementary information for the purposes of IFRS, were submitted to audit procedures conducted together with the audit of the Company’s individual and consolidated financial statements. To form our opinion, we evaluated if these statements are reconciled with the financial statements and accounting records, as applicable, and if their form and content comply with the criteria defined by Accounting Pronouncement CPC 09 – Statement of Value Added. In our opinion, these individual and consolidated statements of value added have been properly prepared, in all material respects, in accordance with the criteria set forth in this Accounting Pronouncement and are consistent with the individual and consolidated financial statements taken as a whole. 

Other information accompanying the individual and consolidated financial statements and the auditor’s report

The executive board is responsible for such other information, which comprises the Management Report.

Our opinion on the individual and consolidated financial statements does not cover the Management Report, and we do not express any form of assurance conclusion thereon.

In connection with our audit of the individual and consolidated financial statements, our responsibility is to read the Management Report and, in doing so, consider whether this report is materially inconsistent with the financial statements or our knowledge obtained in the audit or otherwise appears to be materially misstated. If, based on the work we have performed, we conclude that there is a material misstatement of the Management Report, we are required to report that fact. We have nothing to report in this respect.

Responsibilities of the executive board and those charged with governance for the individual and consolidated financial statements

The executive board is responsible for the preparation and fair presentation of the individual and consolidated financial statements in accordance with the accounting practices adopted in Brazil and with the International Financial Reporting Standards (IFRS) issued by the International Accounting Standards Board (IASB), and for such internal control as the executive board determines is necessary to enable the preparation of financial statements that are free from material misstatement, whether due to fraud or error.

In preparing the individual and consolidated financial statements, the executive board is responsible for assessing the Company’s ability to continue as a going concern, disclosing, as applicable, matters related to going concern and using the going concern basis of accounting unless the executive board either intends to liquidate the Company or to cease operations, or has no realistic alternative but to do so.

Those charged with governance are responsible for overseeing the Company’s and its subsidiaries’ financial reporting process.

Auditor’s responsibilities for the audit of the individual and consolidated financial statements

Our objectives are to obtain reasonable assurance about whether the individual and consolidated financial statements as a whole are free from material misstatement, whether due to fraud or error, and to issue an auditor’s report that includes our opinion. Reasonable assurance is a high level of assurance but is not a guarantee that an audit conducted in accordance with the Brazilian and International Standards on Auditing will always detect a material misstatement when it exists. Misstatements can arise from fraud or error and are considered material if they could, individually or as a whole, reasonably be expected to influence the economic decisions of users made on the basis of these financial statements.

As part of an audit in accordance with the Brazilian and International Standards on Auditing, we exercise professional judgment and maintain professional skepticism throughout the audit. We also:

We communicate with those charged with governance regarding, among other matters, the planned scope and timing of the audit and significant audit findings, including any significant deficiencies in internal control that we identify during our audit.

We also provide those charged with governance with a statement that we comply with relevant ethical requirements, including those regarding independence, and communicate with them all relationships and other matters that may reasonably be thought to bear on our independence, and where applicable, the actions taken to eliminate threats, or the safeguards applied.

From the matters communicated with those charged with governance, we determined those matters that were of most significance in the audit of the financial statements of the current year and are therefore the key audit matters. We describe these matters in our auditor’s report unless law or regulation precludes public disclosure about the matter or when, in extremely rare circumstances, we determine that a matter should not be communicated in our report because the adverse consequences of doing so would reasonably be expected to outweigh the public interest benefits of such communication.

São Paulo, March 16, 2026.

ERNST & YOUNG

Auditores Independentes S/S Ltda.

CRC SP-034519/O

Original report in Portuguese signed by

Uilian Dias Castro de Oliveira

Accountant CRC SP-223185/O

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Management Report

2025 marked the first full cycle following Sabesp’s privatization and consolidated a period of significant transformation for the Company. We advanced with speed, discipline, and consistency, delivering concrete results and strictly executing our universalization plan.

Our conduct was driven by three central priorities:(i) full compliance with the requirements of the new concession agreement (new water and sewage units and service quality indicators), accelerating investments aimed at universalization and strengthening adherence to the regulatory framework; (ii) improving operational and commercial efficiency, increasing standards of quality, reliability, and customer service; and (iii) strengthening financial efficiency and corporate governance across people, processes, and technology.

Throughout the year, we invested R$ 15.2 billion in water supply and sewage infrastructure, surpassing all U-Factor targets for the 2024-2025 cycle. This included achieving 152% of the Water Units target, 133% of the Sewage Units target, and 134% of the Units for Sewage Treatment target. These investments brought health, dignity, and quality of life to approximately 1.8 million people who received access to treated water, 2.1 million who received sewage collection services, and 3.8 million individuals who now have their sewage treated. Additionally, we supported the local economy by generating more than 40,000 direct and indirect jobs during the year.

From an operational standpoint, we achieved significant results, with a 2-point increase in the NPS (Net Promoter Score) compared to 2024, demonstrating continuous improvement in customer experience. We modernized our metering infrastructure, installing approximately 1.5 million new meters this year, while simultaneously securing a contract for what will be the world's largest smart metering project in the water sector: 4.4 million IoT-enabled meters by 2029, supported by R$ 3.8 billion in already contracted investments.

On the corporate front, we advanced the consolidation of the Sabesp’s New Culture and made progress in the ‘Sabesp Gente’ program by welcoming 120 interns, 380 apprentices, and launching our first trainee program, selecting 22 new talents. We optimized our workforce, closing the year with 9,204 employees, a reduction of 13% compared to December 2024. We also completed the first full cycle of Zero-Based Budgeting, redesigning accounts and cost centers and reinforcing our internal governance and budget discipline.

In terms of sustainability, 2025 represents a leap in ambition. We formalized our decarbonization roadmap for 2035, establishing robust targets for absolute and relative reductions in greenhouse gas emissions (41%), even in a context of significant expansion of the volume of sewage treated, in line with universalization goals. As a result, we were honored with recognition from CDP, improving our rating from "C" to "B".

We continue to look to the future with responsibility, urgency, and long-term vision. The acquisition of EMAE represented a decisive step toward strengthening medium and long-term water security. With the Billings reservoir, we will be able to increase our water storage capacity by 52% and integrate essential water and energy assets, generating synergies with structuring programs such as Integra Tietê, which seeks to expand capacity, increase inter-basin transfers, and strengthen resilience to climate variability. In parallel, we expanded our energy transition strategy with self-generation projects totaling 186 MWm, reinforcing financial sustainability, reducing emissions, and increasing predictability in energy costs.

These advances demonstrate how Sabesp is preparing to operate with greater efficiency, resilience, and positive impact in the coming decades, combining structural investments, operational modernization, and strengthened governance. We thank all our stakeholders, including employees, partners, regulators, customers, suppliers, investors, and the communities we serve, for their support, trust, and continuous engagement throughout this transformation.

COMPANY OVERVIEW

Sabesp’s purpose is to connect people to a better future by delivering essential services with excellence and with a strong commitment to public health and environmental preservation. We are one of the largest sanitation companies in the world by number of customers, serving approximately 30 million people with water supply services and 27 million people with sewage collection and treatment services in 2025.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

In addition to operating directly in 375 municipalities, the Company holds minority stakes in three companies that provide water supply and sewage collection and treatment services, as well as six other companies that operate in the energy, paving, and sanitation-related services sectors. Detailed information on these investee companies is presented in Note 12 to the 2025 Financial Statements.

The Company’s shares are listed on the “Novo Mercado” segment of B3 under the ticker “SBSP3” since April 2002, and on the New York Stock Exchange “NYSE”, in the form of Level III American Depositary Receipts “ADRs”, under the ticker “SBS” since May 2002.

PEOPLE AND CULTURE

In 2025, Sabesp advanced in consolidating a New Culture, reinforcing the Company’s identity and supporting the transformations underway. This process was developed through extensive internal listening and analysis, aligning the purpose of connecting people to a better future with practices that ensure operational excellence, socio-environmental responsibility, and positive impact for society.

The New Culture resulted from the active participation of multiple areas and organizational levels, establishing guiding principles that shape our actions: customer focus, trust-based collaboration, ownership with a holistic view, ethics, and purpose-driven execution. More than values, these principles reinforce alignment between strategy and behavior and support a more modern and agile Sabesp, prepared for the challenges of our sector.

In people management, the “Sabesp Gente” Program supported this cultural journey through initiatives aimed at talent attraction, workforce renewal, and sustainable workforce management. In 2025, the Company hired 120 interns, 380 apprentices, and launched its first trainee program, selecting 22 new talents. Sabesp also implemented a new Voluntary Dismissal Program (PDV) to support career transitions. These actions combine the experience of the technical workforce with the energy of new generations, strengthening the Company’s execution capacity throughout the universalization cycle.

Through the New Culture and “Sabesp Gente”, we reinforce an environment where desired behaviors are recognized, talent has opportunities to grow, and decisions are guided by purpose, ethics, and responsibility toward people and future generations. This cultural foundation is essential to ensure that Sabesp continues to advance consistently, aligning operational excellence, sustainability, and the development of its human capital.

SUSTAINABILITY

Sabesp’s ESG strategy advanced significantly in 2025. Under the climate pillar, the Company formalized emission-reduction targets through 2035: (i) 41% reduction in emissions intensity (tCO₂/ ‘000m³ of treated sewage), (ii) 15% reduction in combined total emissions from Scopes 1, 2, and 3, and (iii) 43% reduction in Scope 2 emissions through self-generation and the purchase of clean energy. These targets were established alongside the expansion of treatment volumes, demonstrating that it is possible to grow while reducing carbon intensity.

To enable the energy transition, the Company executed long-term self-generation contracts with Casa dos Ventos (126 MWm) and Engie (60 MWm), in addition to 32 photovoltaic plants already commissioned, totaling 44 MWp in operation. These initiatives reduce costs, volatility, and emissions while strengthening business resilience.

Furthermore, at the Barueri, São Miguel, and Lavapés sewage treatment plants, the Company is advancing the implementation of solutions focused on reducing operating costs and increasing energy efficiency. Key initiatives include: (i) biogas utilization, enabling the generation and use of biogas produced onsite for power generation and for thermal sludge drying using heat from biogas combustion, and (ii) implementation of a sludge pipeline at the Parque Novo Mundo sewage treatment plant, replacing road transport with pipeline transport, which will reduce logistics costs, increase operational reliability, and significantly reduce the Company’s carbon footprint.

From a water-security and resilience perspective, Sabesp continues to strengthen the Integrated Metropolitan System through increased storage capacity, expanded capacity for transfers between systems, production-capacity expansion

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

projects, and indirect water-reuse initiatives. By 2030, the Company expects to add at least 12.8 m³/s of capacity through retrofits, expansions, three indirect reuse projects, reactivation of the Billings–Taiaçupeba interconnection, and the Paraíba do Sul–Alto Tietê transfer, with estimated Capex of R$ 8.2 billion, anticipated from the second tariff cycle.

In governance and transparency, the Company achieved a CDP Climate score of B, an improvement compared to 2024, reflecting progress in managing climate-related risks and opportunities.

EXTERNAL AUDIT SERVICES

In the fiscal year ended December 31, 2025, the Company did not engage any services other than audit services from its external auditors.

ECONOMIC AND FINANCIAL PERFORMANCE

In 2025, Sabesp reached R$ 37.6 billion in net revenue (+4% vs. 2024) and R$ 8.5 billion in Net Income (-12% vs. 2024). It is important to note that, in 2024, the bifurcation of the financial asset generated a gain of approximately R$ 5.5 billion in the Company’s Net Income. Adjusting for the effect of financial asset remeasurement, the Company’s Net Income amounted to R$ 6.3 billion, an increase of 22% y/y. Finally, the Company announced the distribution of R$ 1.8 billion to its shareholders in IoE ("Interest on Equity").

Financial Asset Bifurcation (Indemnity)

In 2024, following the completion of the privatization process and the execution of the agreement with URAE-1 on July 23, 2024, the Company recognized the bifurcation of the financial asset related to concession assets, previously classified solely as intangible assets. The financial asset corresponds to reversible investments that are not fully amortized by the end of the contract term (October 2060), which will be indemnified as set forth in the URAE-1 agreement. The recognition of this financial asset generated the following impacts in 2024: R$ 9,161 million in gross revenue and R$ 5,481 million in net income. For further information, refer to Note 16 of the 2024 Financial Statements.

Net revenue from sanitation services increased 2.2% y/y in 2025, reaching R$ 22.2 billion, explained by:

· +3.7% in net price: removal of discounts to large clients (“Demanda Firme”);

· +2.4% in billed volume: growth in new units;

· (1.8)% in mix: increase in vulnerable customers eligible for subsidized tariffs (from 2.0 million to 3.2 million registered customers, annual average);

· (2.1)% FAUSP: in 2024 FAUSP began only in the second half of the year and the rate was revised in August 2025

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

ADMINISTRATIVE COSTS AND EXPENSES

In 2025, costs and expenses reached R$ 11.2 billion, an improvement of 13.8% compared to 2024, mainly due to developments in the following lines: (i) general expenses (-54.5% y/y) related to advance transfers to municipal funds (FMSAI); (ii) general materials (-29.3% y/y) due to process standardization and contract reviews throughout the year; and (iii) personnel (-9.9% y/y) due to a 13% reduction in the workforce.”

INVESTMENTS

In 2025, capex totaled R$ 15,202 million, an increase of 120% compared to the same period of the previous year. By the end of the first tariff cycle, in 2029, the Company estimates approximately R$ 70 billion in investments to achieve the universalization of water supply and sewage services across the 371 municipalities that comprise URAE-1.

LEVERAGE AND CAPITAL STRUCTURE

In 2025, Sabesp issued R$ 18.7 billion in debt instruments to finance investments related to universalization. In addition, 2025 was focused on reducing the cost of debt, which closed the year at CDI – 0.20%, and on extending maturities, with an average debt maturity of 5.6 years at the end of 2025.

Even with the year’s borrowings, the Company’s Leverage Ratio increased only 5p.p. y/y, supported by strong cash generation during the period. The net debt/Adjusted EBITDA ratio ended the year at 2.2x, a healthy level for companies in the sector.

The Company believes that its capital structure is well suited to its operations and industry. Historically, these capitalization metrics have enabled the Company to access official and multilateral banks, manage current investment levels, and maintain a favorable debt profile, characterized by long-term, low-cost financing.

As of December 31, 2025, the Company’s equity reached R$ 42.4 billion (+15% vs. 2024). This increase was driven by retained earnings generated in 2025.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

PAYMENT OF INTEREST ON EQUITY (IoE)

On December 18, 2025, the Board of Directors approved the crediting of Interest on Equity in the total gross amount of R$ 1,798,000, corresponding to R$ 2.643892990 per share, to be paid on April 30, 2026, as per the Notice to the Market.

SHARES BUYBACK PROGRAM

On May 12, 2025, the Board of Directors approved the Share Repurchase Plan, authorizing the acquisition of up to 6,904,170 common shares (approximately 1% of the total, on a fully diluted basis) for a period of 18 months (from 05/13/2025 to 11/12/2026). The primary purpose of the program is to serve the Company’s long-term incentive plans (Restricted Shares and Performance Shares) approved on 04/29/2025, while also allowing the Company to hold shares in treasury for future cancellation or sale. On the date of approval, the Company’s share capital consisted of 683,509,868 common shares (and 1 golden share), with no treasury shares. Shares buyback were and will continue to be carried out on B3’s trading platform.

Based on the shareholding position as of December 31, 2025, the Company held: (a) 703,773,869 outstanding shares, as defined under Article 67 of CVM Resolution No. 80/22; and (b) 3,554,431 treasury shares, representing approximately 0.5% of the Company’s total outstanding shares.

CAPITAL INCREASE

At the same meeting held on December 18, 2025, the Board of Directors approved a capital increase in the amount of R$ 2,810,000, within the limit of the authorized capital, through the capitalization of part of the balance of profit reserves, with the issuance of 20,264,000 new common shares (registered, book-entry, and with no par value). These shares will be granted free of charge to shareholders at the ratio of 0.029646975 new share for each common share held as of the shareholding position on 12/23/2025, pursuant to Article 169 of Law 6,404/76. The capitalized profits relate to periods prior to 2024. 

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Statements of Financial Position as of December 31, 2025 and 2024

In thousands of reais

The accompanying notes are an integral part of these financial statements.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Statements of Financial Position as of December 31, 2025 and 2024

In thousands of reais

The accompanying notes are an integral part of these financial statements.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Statements of Income for the

Years ended December 31, 2025 and 2024

In thousands of reais, unless otherwise stated

The accompanying notes are an integral part of these financial statements.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Statements of Comprehensive Income for the

Years ended December 31, 2025 and 2024

In thousands of reais

The accompanying notes are an integral part of these financial statements.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Statement of Changes in Equity for the

Years ended December 31, 2025 and 2024

In thousands of reais, unless otherwise stated

The accompanying notes are an integral part of these financial statements.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Statements of Cash Flows for the

Years ended December 31, 2025 and 2024

In thousands of reais (continued)

The accompanying notes are an integral part of these financial statements.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Statements of Value Added for the

Years ended December 31, 2025 and 2024

In thousands of reais (continued)

The accompanying notes are an integral part of these financial statements.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP
Notes to the Financial Statements for the Years ended December 31, 2025 and 2024 In thousands of reais, unless otherwise stated

Companhia de Saneamento Básico do Estado de São Paulo (“SABESP” or “Company”) is a publicly-held company headquartered in the municipality of São Paulo, at Rua Costa Carvalho, 300, CEP 05429-900. 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.

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 financial statements were approved by the Board of Directors on March 16, 2026.

The Company's financial statements were prepared and are being presented in accordance with 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), and which were approved by the Brazilian Securities and Exchange Commission (“CVM”). All material information related to the financial statements, and this information alone, is being disclosed and corresponds to the information used by the Company’s Management in its administration.

The financial statements were prepared based on historical cost, except for certain financial instruments measured at their fair values when required by the standards.

The preparation of the financial statements, in compliance with IFRS and CPCs, requires the use of certain essential accounting estimates. In addition, it requires Management to exercise its judgment in the process of applying the Company's accounting policies. The areas that involve a greater degree of judgment or complexity or which assumptions and estimates are significant to the financial statements are described in Note 6.

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

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

The accounting practices are presented in the respective notes for a better understanding of the recognition and measurement basis applied in the preparation of the financial statements.

The consolidated financial statements comprise the financial statements of the Company and its subsidiaries as of December 31, 2025. The Company controls an entity when (i) it has power over the investee; (ii) it is exposed or is

Companhia de Saneamento Básico do Estado de São Paulo – SABESP
Notes to the Financial Statements for the Years ended December 31, 2025 and 2024 In thousands of reais, unless otherwise stated

entitled to the variable returns arising from its involvement with the investee; and (iii) it has the ability to use this power to influence its returns.

When the Company does not hold the majority of the voting rights in an investee, it will have power over the investee when the voting rights are sufficient to effectively enable it to conduct the relevant activities of the investee unilaterally.

The financial statements of the subsidiary are included in the consolidated financial statements from the date on which the Company obtains control until the date on which this control ceases to exist. The revenues and expenses of a subsidiary acquired or disposed of during the year are included in the income statement from the date on which the Company obtains control until the date on which the Company ceases to control the subsidiary.

The consolidated financial statements were prepared for the same reporting date of the individual financial statements.

All intra-group balances, revenues and expenses and unrealized gains and losses arising from intra-group transactions were eliminated. The other comprehensive income of the subsidiaries, when applicable, will be recorded directly in the Company's equity under "other comprehensive income".

In the individual financial statements, the investments of the Company in its subsidiaries are accounted for based on the equity accounting method.

For details of the consolidation basis, as well as the Company's percentage interest in its subsidiaries, see Note 12.

This statement is intended to show the wealth generated by the Company and its distribution during a given period and is presented as required by accounting practices adopted in Brazil, as supplementary information to the financial statements for IFRS purposes.

The DVA was prepared based on information obtained from the accounting records that support the preparation of the financial statements. The first part presents the wealth created by the Company represented by revenue, inputs purchased from third parties and retentions, as well as the wealth received in transfer, represented by equity accounting and financial income. The second part presents the value added distribution among personnel, taxes, fees and contributions, value distributed to providers of capital and value distributed to shareholders.

Items included in the financial statements are measured using the currency of the primary economic environment in which the entity operates (“functional currency”). The functional currency of the parent company and the presentation currency of the Company's individual and consolidated financial statements is the Brazilian real. Each group entity determines its own functional currency, and in those whose functional currencies are different from the real, the financial statements are translated into the real on the reporting date.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP
Notes to the Financial Statements for the Years ended December 31, 2025 and 2024 In thousands of reais, unless otherwise stated

Transactions in foreign currency are initially recorded at the exchange rate of the functional currency in effect at the date of the transaction. Monetary assets and liabilities denominated in foreign currency are translated using the closing exchange rate at the reporting date.

Foreign exchange gains and losses resulting from the settlement of these transactions and the translation of monetary assets and liabilities denominated in foreign currency are recognized in the income statement, except for borrowings and financing that are related to property, plant and equipment or intangible assets in progress, and foreign exchange losses are recognized against the asset itself while it is in progress, as described in the accounting policy of Note 17.

The amendments to CPC 02 (R2) / IAS 21 – The Effects of Changes in Foreign Exchange Rates; CPC 37 (R1) / IFRS 1 – First-time Adoption of International Financial Reporting Standards; CPC 18 (R3) / IAS 28 – Investments in Associates, Subsidiaries and Joint Ventures; ICPC 09 – Separate Financial Statements, Consolidated Financial Statements and Application of the Equity Method; and OCPC 10 – Carbon Credits (tCO2e), Emission Allowances, and Decarbonization Credits (CBIO), did not have any impact on the disclosures or amounts recognized in the annual financial statements.

The Company has not adopted in advance and is evaluating the impacts on the disclosures or amounts recognized in the financial statements related to the following new and revised IFRSs that management deems applicable to the Company:

Companhia de Saneamento Básico do Estado de São Paulo – SABESP
Notes to the Financial Statements for the Years ended December 31, 2025 and 2024 In thousands of reais, unless otherwise stated

Companhia de Saneamento Básico do Estado de São Paulo – SABESP
Notes to the Financial Statements for the Years ended December 31, 2025 and 2024 In thousands of reais, unless otherwise stated

There are no other standards and interpretations issued and not yet adopted that may, in the Management’s opinion, have a significant impact on the profit or loss for the year or on the equity disclosed by the Company in its financial statements.

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.

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, at more attractive interest rates in US Dollar, Euro and Yen.

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

Companhia de Saneamento Básico do Estado de São Paulo – SABESP
Notes to the Financial Statements for the Years ended December 31, 2025 and 2024 In thousands of reais, unless otherwise stated

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 financial debt in the amount of R$ 10,632,252 as of December 31, 2025 (R$ 3,356,365 as of December 31, 2024), is indexed to the U.S. dollar, Euro and Yen. The exposure to currency risk is as follows:

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

As of December 31, 2025, if the Brazilian real had depreciated or appreciated by 10 percentage points, against the U.S. dollar, Yen and Euro with all other variables held constant, the effects on profit or loss before borrowing costs and taxes, for the year ended December 31, 2025 would have been R$ 1,063,311 (R$ 336,672 for the year ended December 31, 2024), upwards or downwards, excluding the effects of to the hedging instruments (Note 19).

The Company understands that it could comfortably accommodate any devaluation scenario due to derivative financial instruments such as cross-currency swaps already contracted.

Interest rate risk

It is the risk that the fair value of the future cash flows of a financial instrument will fluctuate due to variations in market interest rates. For most transactions, the Company manages the interest rate risk by entering into derivative financial instruments that effectively swap their exposures for liabilities indexed to the CDI.

The table below shows the borrowings and financing subject to different inflation adjustment indices, including the derivative instrument:

Companhia de Saneamento Básico do Estado de São Paulo – SABESP
Notes to the Financial Statements for the Years ended December 31, 2025 and 2024 In thousands of reais, unless otherwise stated

Another risk to which the Company is exposed is the mismatch of inflation adjustment indices of its debts with those of its service revenues and financial assets, adjusted by the IPCA. Tariff adjustments of services provided do not necessarily follow the increases in the adjustments indices of borrowings, financing, and interest rates affecting indebtedness.

As of December 31, 2025, if interest rates on borrowings and financing had been 1 percentage point higher or lower with all other variables held constant, the effects on consolidated profit before taxes for the year ended December 31, 2025 would have been R$ 339,248 (R$ 234,384 for the year ended December 31, 2024), upwards or downwards, mainly as a result of lower or higher interest expenses on floating rate borrowings and financing.

The table below shows the sensitivity analysis of the financial instruments, prepared under CPC 40 (R1)/ IFRS 7, to evidence the balances of main financial assets and liabilities, calculated at a rate projected for the twelve-month period after December 31, 2025, or until the final settlement of each contract, whichever occurs first, considering a probable scenario.

The purpose of the sensitivity analysis is to measure the impact of changes in the market on the financial instruments, considering all other variables constant. At the time of settlement, the amounts may be different from those presented, due to the estimates used in the measurement.

The table below considers the impact of the derivative instrument: