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

PUBLICLY HELD COMPANY

CNPJ 43.776.517/0001-80

NIRE nº 35.3000.1683-1

MATERIAL FACT

Companhia de Saneamento Básico do Estado de São Paulo – Sabesp (“Company” or “Sabesp”), in compliance with Article 157, §4º, of Law 6.404/76, and with Resolution of the Brazilian Securities Commission ("CVM") 44, dated August 23, 2021, informs its shareholders and the market in general as follows.

With respect to the buyback plan for the acquisition of up to six million, nine hundred and four thousand, one hundred and seventy (6,904,170) common shares issued by the Company (“Buyback Plan”), representing, on a fully diluted basis, approximately one percent (1%) of the total outstanding shares and of the free float, approved by the Board of Directors at a meeting held on May 12, 2025, as disclosed in the Material Fact released on the same date, Sabesp clarifies that the Buyback Plan has not yet commenced, as Sabesp is in the process of hiring the financial institutions that will act as intermediaries under the referred plan.

In this regard, Sabesp informs that the Buyback Plan will only commence after the engagement of such intermediary institutions and the disclosure of a new Material Fact disclosing the completion of said engagement, together with the resubmission of Annex G to CVM Resolution No. 80, dated March 29, 2022.

São Paulo, May 14, 2025

DANIEL SZLAK

Chief Financial and Investor Relations Officer 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.