sbs20180621_6k2.htm - Generated by SEC Publisher for SEC Filing

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 June, 2018

(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

CNPJ nº 43.776.517/0001-80
NIRE nº 35.3000.1683-1

MATERIAL FACT

23rd DEBENTURES ISSUANCE

Companhia de Saneamento Básico do Estado de São Paulo – Sabesp (“SABESP” or “Company”), pursuant to the provisions of Article 157, Paragraph 4 of Law 6.404/76 and the provisions of Brazilian Securities and Exchange Commission (“CVM”) Instruction 358, dated as of January 3, 2002, as amended, hereby informs its shareholders and the market in general that, the Board of Directors, in a meeting held on June 21, 2018, approved the 23rd issuance of simple, unsecured and non-convertible debentures, in up to three series, for public distribution, with restricted distribution efforts, pursuant to CVM Rule No. 476, dated as of January 16, 2009, as amended (“CVM Rule 476”), in the total amount of up to seven hundred fifty thousand million reais (R$ 750,000,000.00) (“Debentures” and “Offer”, respectively), being the Offer conditioned to the issuance of, at least, five hundred thousand (500,000) Debentures, in the total amount of five hundred million reais (R$500,000,000.00). The issuance of each of the series, the number of Debentures to be placed in each serie, the remuneration of the Debentures and the total amount of the Offer will be defined according to the bookbuilding process, in the communicating vessels system.

The Offer will target professional investors only, in compliance with Article 9-A of CVM Rule 539, of November 13, 2013, as amended, and Article 2 of CVM Rule 476. According to Article 3 of CVM Rule 476, the Offer will be presented to a maximum of seventy-five (75) professional investors, though the Debentures may only be subscribed by a maximum of fifty (50) professional investors. The process of structuring of the Offer and distribution of the Debentures will be undertaken by a consortium of financial institutions belonging to the Securities Distribution System.

The proceeds from the issuance and offering of the Debentures will be used to refinance its financial commitments maturing in 2018 and to the Company's cash flow increment.

São Paulo, June 21, 2018.

Rui de Britto Álvares Affonso

Chief Financial Officer 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: June 21, 2018

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

By:	/s/ Rui de Britto Álvares Affonso
	Name: Rui de Britto Álvares Affonso 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.