6-K

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 6-K

REPORT OF FOREIGN ISSUER PURSUANT TO RULE 13a-16 OR 15d-16 OF THE

SECURITIES EXCHANGE ACT OF 1934

For May, 2025 (Commission File No. 1-31317)

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 Sao Paulo - SABESP

(Translation of Registrant's name into English)

Rua Costa Carvalho, 300 São Paulo, S.P., 05429-900 Federative Republic of Brazil

(Address of Registrant's principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F.

Form 20-F ___X___ Form 40-F ______

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1)__.

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7)__.

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___

If "Yes" is marked, indicated below the file number assigned to the registrant in connection with Rule 12g3-2(b):

COMPANHIADE SANEAMENTO BÁSICO DO ESTADO DE SÃO PAULO – SABESP

PUBLICLYHELD COMPANY

CNPJ 43.776.517/0001-80

NIRE nº 35.3000.1683-1

NOTICETO THE MARKET

Companhia de Saneamento Básico do Estado de SãoPaulo – Sabesp (“Company” or “Sabesp”), in compliance with the provisions of the Brazilian Securities and Exchange Commission (“CVM”) Resolution No. 44, dated August 23, 2021, and Article 28 of CVM Resolution No. 23, dated February 2021, informs its shareholders and the market in general that its Board of Directors, in a meeting held on May 12, 2025, approved the hiring of Ernst & Young Auditores Independentes S/S Ltda. ("EY") as the independent auditing firm responsible for auditing the annual financial statements and reviewing the Company's quarterly financial information, replacing BDO RCS Auditores Independentes – Sociedade Simples Limitada (“BDO”), which had been responsible for providing these services until then. This change aims to synchronize the work and avoid duplication of efforts in obtaining and providing documents, as EY already provides auditing services to the Company's reference investor. BDO will continue to support the Company in other activities.

The services provided by EY will commence with the review of the financial information for the quarter ending June 30, 2025. The approval of EY's hiring considered the favorable opinion of the Audit Committee, issued in a meeting held on May 7, 2025, and had the consent of BDO.

São Paulo, May 21, 2025

DANIEL SZLAK

Chief Financial and Investor Relations Officer

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized, in the city São Paulo, Brazil.

Date: May 21, 2025

FORWARD-LOOKING STATEMENTS

This press release may contain forward-looking statements. These statements are statements that are not historical facts, and are based on management's current view and estimates of future economic circumstances, industry conditions, company performance and financial results. The words "anticipates", "believes", "estimates", "expects", "plans" and similar expressions, as they relate to the company, are intended to identify forward-looking statements. Statements regarding the declaration or payment of dividends, the implementation of principal operating and financing strategies and capital expenditure plans, the direction of future operations and the factors or trends affecting financial condition, liquidity or results of operations are examples of forward-looking statements. Such statements reflect the current views of management and are subject to a number of risks and uncertainties. There is no guarantee that the expected events, trends or results will actually occur. The statements are based on many assumptions and factors, including general economic and market conditions, industry conditions, and operating factors. Any changes in such assumptions or factors could cause actual results to differ materially from current expectations.