Companhia de Saneamento Basico do Estado de Sao Paulo–SABESP ADR 2026年年度报告和过渡报告

FORM 20-F REGISTRATION STATEMENT PURSUANT TO SECTION 12(b) OR 12(g) OF THE SECURITIES EXCHANGE ACTOF 1934 OR ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 FORTHE FISCAL YEAR ENDED DECEMBER 31, 2025 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 OR SHELL COMPANY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF1934 Commission file number: 001-31317 Companhia de Saneamento Básico do Estado de São Paulo-SABESP(Exact name of Registrant as specified in its charter) Basic Sanitation Company of the State of São Paulo-SABESPThe Federative Republic of Brazil(Translation of Registrant’s Name into English)(Jurisdiction of Incorporation or Organization) Rua Costa Carvalho, 30005429-900 São Paulo, SP, Brazil(Address of principal executive offices) Daniel SzlakRua Costa Carvalho, 30005429-900 São Paulo, SP, BrazilTelephone: +55 11 3388 8000Email: dri@sabesp.com.br(Name, Telephone, E-mail and/or Facsimile number and Address of Company Contact Person) Securities registered or to be registered pursuant to Section 12(b) of the Act: TradingSymbol(s)Not tradedSBS *Shares are not listed for trading, but only in connection with the registration of American Depositary Receipts pursuant to the requirements of the New York StockExchange. Securities registered or to be registered pursuant to Section 12(g) of the Act: None Securities for which there is a reporting obligation pursuant to Section 15(d) of the Act: None Indicate the number of outstanding shares of each of the issuer’s classes of capital or common stock as of December 31, 2025:700,219,438shares of common stock and one share of preferred stock Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. YesNo If this report is an annual or transition report, indicate by check mark if the registrant is not required to file reports pursuant to Section13 or 15(d) of the Securities Exchange Act of 1934. YesNo Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the SecuritiesExchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports),and (2) has been subject to such filing requirements for the past 90 days. YesNo Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submittedpursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that theregistrant was required to submit such files). YesNo Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or an emerginggrowth company. See definition of “large accelerated filer,” “accelerated filer,” and “emerging growth company” in Rule 12b-2 of theExchange Act. (Check one): Large Accelerated Filer Accelerated Filer Non-accelerated Filer Emerging Growth Company☐ If an emerging growth company that prepares its financial statements in accordance with U.S. GAAP, indicate by check mark if theregistrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards†provided pursuant to Section 13(a) of the Exchange Act. † The term “new or revised financial accounting standard” refers to any update issued by the Financial Accounting Standards Board toits Accounting Standards Codification after April 5, 2012. Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectivenessof its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registeredpublic accounting firm that prepared or issued its audit report. If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of theregistrant included in the filing reflect the correction of an error to previously issued financial statements. Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-basedcompensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). Indicate by check mark which basis of accounting the registrant has used to prepare the financial statements included in this filing:U.S. GAAPInternational Financial ReportingOther Standards as issued by theInternational Accounting StandardsBoard If “Other” has been checked in response to the previous question, indicate by check mark which financial statement item the registranthas elected to follow. Item 17Item 18 If this is an annual report, indicate by check mark whether the registrant is a shell