Sabesp (NYSE: SBS) wins ARSESP nod for 6.5% rate increase, 10.6% equilibrium uplift

Rhea-AI Filing Summary

Companhia de Saneamento Básico do Estado de São Paulo – Sabesp reports that regulator ARSESP has approved a tariff adjustment for its water and sewage services. The resolution authorizes an average increase of 6.5% on the current rates charged to users, effective from January 1, 2026. According to Sabesp’s preliminary review, this corresponds to a 10.6% increase in its equilibrium rate, which is a benchmark level designed to balance revenues with operating and investment needs.

The company plans to provide further clarification on the main items behind this adjustment and has noted that ARSESP also published a technical note and an Excel model detailing the calculation. Sabesp states it will keep shareholders and the market informed about any additional developments related to this rate change.

Positive

• Regulatory approval of higher tariffs: ARSESP authorized an average 6.5% increase in Sabesp’s user rates from January 1, 2026, which the company estimates as a 10.6% rise in its equilibrium rate, potentially supporting future revenue and cash generation.

Negative

• None.

Insights

Utilities and Regulatory Analyst

Regulator approves meaningful Sabesp tariff increase effective January 2026.

Sabesp has received approval from ARSESP for an average 6.5% increase in user tariffs starting on January 1, 2026. Management’s preliminary reading is that this equates to a 10.6% rise in the company’s equilibrium rate, the level intended to align revenues with costs and required returns.

For a regulated utility, a double‑digit equilibrium rate uplift can support revenue growth and help offset inflationary or investment pressures, depending on actual demand and collection. The financial impact will depend on how the new tariffs flow through Sabesp’s customer base and operating structure once they become effective.

Investors may focus on the detailed technical note and Excel model published by ARSESP, as well as Sabesp’s forthcoming clarifications, to better understand the drivers of the adjustment and how it may affect results after January 1, 2026.

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 December, 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):

COMPANHIA DE SANEAMENTO BÁSICO DO ESTADO DE SÃO PAULO – SABESP Publicly-held company CNPJ nº 43.776.517/0001-80 NIRE nº 35.3000.1683-1 FATO RELEVANTE Companhia de Saneamento Básico do Estado de São Paulo – Sabesp (“Company” or “Sabesp”), in compliance with the provisions of the Brazilian Securities Commission (“CVM”) Resolution No. 44, dated August 23, 2021, as amended, informs its shareholders and the market in general that ARSESP Resolution No. 1,748/2025 (“Resolution”) has been published in the State Official Gazette. According to the Resolution, the Company is authorized to apply an average adjustment of 6.5% to the current rates charged to users, effective as of January 1, 2026. Based on a preliminary review by the Company, this amount represents an increase of 10.6% in the equilibrium rate. Sabesp will work throughout the day to provide further clarification on the main items of the rate adjustment and will keep the market informed of any developments. Along with the Resolution, a Technical Note and an Excel Model were also published, which can be accessed directly on ARSESP’s website. The Company will keep its shareholders and the market informed of any developments in this matter. São Paulo, December 2, 2025. DANIEL SZLAK CFO and IRO

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: December 2, 2025

Companhia de Saneamento Básico do Estado de São Paulo - SABESP
By:	/s/  Daniel Szlak
	Name: Daniel Szlak Title: Chief Financial Officer and Investor Relations Officer

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.

FAQ

What did Sabesp (SBS) announce in this Form 6-K?

Sabesp announced that regulator ARSESP published a resolution authorizing the company to apply an average 6.5% adjustment to the rates charged to its users, effective from January 1, 2026.

How large is the Sabesp tariff increase approved by ARSESP?

The resolution authorizes Sabesp to implement an average 6.5% increase on current rates. Sabesp’s preliminary assessment indicates this corresponds to a 10.6% increase in the equilibrium rate.

When will Sabesp’s new rates come into effect?

The new Sabesp rates authorized by ARSESP are effective as of January 1, 2026, meaning the updated tariffs will apply from the beginning of 2026.

What is the equilibrium rate mentioned by Sabesp in the filing?

Sabesp states that the approved adjustment represents a 10.6% increase in the company’s equilibrium rate, which is a reference level intended to balance operating costs, investments and allowed returns in the regulatory framework.

Where can investors find the technical details of Sabesp’s rate adjustment?

Alongside ARSESP’s resolution, a Technical Note and an Excel Model were published and can be accessed directly on ARSESP’s website, providing more detail on how the rate adjustment was calculated.

How does Sabesp plan to update the market about this tariff decision?

Sabesp stated it will work to provide further clarification on the main items of the rate adjustment and will keep shareholders and the market informed of any developments related to this matter.