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, 2026

(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

Quarterly Financial Information for

the period ended March 31, 2026

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statements of Financial Position as of March 31, 2026 and December 31, 2025

In thousands of reais

		Individual		Consolidated
	Note	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025

Current Assets
Cash and cash equivalents	7	3,155,200	4,569,998	3,540,240	4,663,226
Financial investments	8	15,537,279	7,693,630	15,641,914	7,707,745
Trade receivables	10 (a)	4,518,755	4,406,829	4,571,688	4,413,449
Accounts receivable from related parties	11 (a)	276,021	276,282	276,096	276,388
Inventories		125,569	21,863	125,780	22,061
Restricted cash	9	17,864	9,575	17,864	9,575
Taxes Recoverable	20 (a)	1,436,108	1,295,237	1,540,437	1,295,310
Assets held for sale		48,150	26,864	48,150	26,864
Other assets		173,748	159,500	187,137	141,892
Total current assets		25,288,694	18,459,778	25,949,306	18,556,510

Non-current Assets
Trade receivables	10 (a)	367,159	258,544	367,159	258,544
Accounts receivable from related parties	11 (a)	852,234	862,782	852,234	862,782
Escrow Deposits		128,989	120,021	190,446	120,021
Deferred income and social contribution taxes	22 (a)	—	—	41,513	—
Taxes Recoverable	20 (a)	—	—	267,575	—
Other assets		32,503	33,509	32,502	33,509

Investments	12	1,479,309	494,088	243,146	254,358
Investment properties		11,478	49,933	328,066	49,933
Contract asset and other concession assets	13	14,255,616	11,006,489	14,268,245	11,018,516
Financial Asset of the Concession	15	22,125,879	21,665,330	22,321,254	21,665,330
Intangible assets	14	50,071,845	50,354,751	50,732,495	50,492,473

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statements of Financial Position as of March 31, 2026 and December 31, 2025

In thousands of reais

Property, plant, and equipment	16	915,655	890,791	1,124,763	890,791
Total non-current assets		90,240,667	85,736,238	90,769,398	85,646,257

Total Assets		115,529,361	104,196,016	116,718,704	104,202,767

		Individual		Consolidated
	Note	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025

Current Liabilities
Trade payables and contractors		842,069	2,398,445	872,111	2,400,046
Services payable	27	2,598,708	2,767,899	2,601,742	2,772,416
Borrowings and financing	17	4,884,127	5,132,890	4,872,680	5,092,816
Labor and social obligations	25	407,495	699,629	435,732	699,629
Taxes and contributions payable	20 (b)	292,239	614,078	303,085	615,592
Deferred PIS/Cofins taxes	21	81,432	89,049	81,432	89,049
Dividends and interest on capital payable	28	2,059,850	2,059,850	2,063,503	2,059,850
Provisions	23 (a)	1,380,446	1,370,013	1,380,446	1,370,013
Public-Private Partnership - PPP	14 (c)	473,049	469,687	473,049	469,687
Derivative financial instruments	19	1,142,171	521,832	1,484,755	661,421
Performance Agreements	14 (f)	125,766	120,776	125,766	120,776
Other liabilities		218,446	201,620	228,068	201,619
Total current liabilities		14,505,798	16,445,768	14,922,369	16,552,914

Non-current Liabilities
Borrowings and financing	17	47,114,306	35,168,713	46,769,945	35,049,531
Deferred income and social contribution taxes	22 (a)	3,076,274	3,129,908	3,076,274	3,129,908
Deferred PIS/Cofins	21	1,218,870	1,191,916	1,218,870	1,191,916
Provisions	23 (a)	537,877	533,399	711,943	533,399

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statements of Financial Position as of March 31, 2026 and December 31, 2025

In thousands of reais

Pension plan obligations	26	2,136,163	2,140,161	2,407,944	2,140,161
Public-Private Partnership - PPP	14 (c)	2,851,931	2,856,008	2,851,931	2,856,008
Performance Agreements	14 (f)	3,543	6,151	3,543	6,151
Contract liabilities	24	—	—	626,985	—
Other liabilities		383,643	322,868	304,875	341,655
Total non-current liabilities		57,322,607	45,349,124	57,972,310	45,248,729

Total liabilities		71,828,405	61,794,892	72,894,679	61,801,643

Equity
Capital stock		21,379,216	21,210,000	21,379,216	21,210,000
Capital reserves		65,843	30,219	65,843	30,219
Earnings reserves		21,348,996	21,518,212	21,348,996	21,518,212
Treasury shares		(475,385)	(475,385)	(475,385)	(475,385)
Equity valuation adjustments		117,652	118,078	117,652	118,078
Retained earnings		1,264,634	—	1,264,634	—
Total Equity - Controlling		43,700,956	42,401,124	43,700,956	42,401,124
Non-Controlling Shareholders		—	—	123,069	—
Total equity	28	43,700,956	42,401,124	43,824,025	42,401,124

Total Liabilities and Equity		115,529,361	104,196,016	116,718,704	104,202,767

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statements of Income for the

Periods ended March 31, 2026 and 2025

In thousands of reais, unless otherwise stated

		Individual		Consolidated
	Note	January to March 2026	January to March 2025	January to March 2026	January to March 2025

Net operating revenue	31	9,954,560	8,416,021	9,964,842	8,426,200
Operating costs	32	(6,044,720)	(4,894,875)	(6,049,315)	(4,905,642)

Gross profit		3,909,840	3,521,146	3,915,527	3,520,558

Selling expenses	32	(150,560)	(172,053)	(150,846)	(172,297)
Allowance for doubtful accounts	10 (c)	(53,493)	(136,407)	(53,602)	(136,699)
Administrative expenses	32	(314,963)	(399,244)	(316,898)	(397,138)
Other operating income (expenses), net	34	(19,800)	18,123	(18,827)	18,124
Equity accounting	12	12,112	12,567	8,311	11,348

Profit from operations before financial income (expenses)		3,383,136	2,844,132	3,383,665	2,843,896

Financial income, net	33	(1,027,004)	(594,447)	(1,026,100)	(592,970)

Profit before income and social contribution taxes		2,356,132	2,249,685	2,357,565	2,250,926

Income and social contribution taxes
Current	22 (c)	(660,735)	(694,920)	(662,168)	(696,161)
Deferred	22 (c)	53,634	(72,673)	53,634	(72,673)
		(607,101)	(767,593)	(608,534)	(768,834)

Profit for the period		1,749,031	1,482,092	1,749,031	1,482,092
Earnings per share - basic and diluted (in reais)	29	0.50	0.43	0.50	0.43

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statements of Comprehensive Income for the

Periods ended March 31, 2026 and 2025

In thousands of reais, unless otherwise stated

		Individual and Consolidated
	Note	January to March 2026	January to March 2025

Profit for the period		1,749,031	1,482,092
Items which will be subsequently reclassified to the income statement:		(426)	(12,226)
Retained earnings (accumulated losses) on cash flow hedge, net of taxes	19	—	(12,226)
Other adjustments		(426)	—
Total comprehensive income for the period		1,748,605	1,469,866

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statement of Changes in Equity for the

Periods ended March 31, 2026 and 2025

In thousands of reais, unless otherwise stated

		Earnings reserves
	Note	Capital stock	Treasury shares	Capital Reserve	Legal reserve	Investment reserve	Retained Earnings/ Accumulated Losses	Equity valuation adjustments	Non- Controlling Shareholders	Total
Individual and Consolidated
Balances as of December 31, 2024		15,000,000	-	-	2,343,583	19,304,132	—	280,339	—	36,928,054
Profit for the period		-	-	-	-	-	1,482,092	-	-	1,482,092
Gains and losses on financial instruments		-	-	-	-	-	-	(12,226)	-	(12,226)
Total comprehensive income/(loss) for the period		-	-	-	-	-	1,482,092	(12,226)	-	1,482,092
Capital increase		3,400,000	-	-	-	(3,400,000)	-	-	-	-
Balances as of March 31, 2026		18,400,000	-	-	2,343,853	15,904,132	1,482,092	268,113	-	38,397,920

Balances as of December 31, 2025		21,210,000	(475,385)	30,219	2,766,686	18,751,526	—	118,078	—	42,401,124
Profit for the period		—	—	—	—	—	1,749,031	—	—	1,749,031
Other adjustments		—	—	—	—	—	—	(426)	—	(426)
Total comprehensive income/(loss) for the period		—	—	—	—	—	1,749,031	(426)	—	1,748,605
Capital increase	28 (a)	169,216	—	—	—	(169,216)	—	—	—	—
Long-Term Incentive Plan	28 (b)	—	—	35,624	—	—	—	—	—	35,624
Addition of non-controlling interest arising from business combination	4	—	—	—	—	—	—	—	417,090	417,090
Acquisition of non-controlling interest	4	—	—	—	—	—	(484,397)	—	(294,021)	(778,418)
Balances as of March 31, 2026		21,379,216	(475,385)	65,843	2,766,686	18,582,310	1,264,634	117,652	123,069	43,824,025

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statements of Cash Flows for the

Periods ended March 31, 2026 and 2025

In thousands of reais, unless otherwise stated

	Individual		Consolidated
	January to March 2026	January to March 2025	January to March 2026	January to March 2025
Cash flows from operating activities
Profit before income and social contribution taxes	2,356,132	2,249,685	2,357,565	2,250,926
Adjustments for reconciliation of net income:
Depreciation and amortization	696,237	582,326	697,472	583,560
Residual value of property, plant and equipment, intangible assets and investment properties written-off	1,587	934	1,587	934
Allowance for doubtful accounts	53,493	136,407	53,602	136,699
Provisions and inflation adjustments on provisions	29,833	158,411	29,833	158,411
Interest calculated on borrowings and financing payable	1,292,903	646,698	1,292,903	646,698
Interest and inflation adjustments, net	(546,103)	(159,898)	(547,396)	(160,113)
Derivative financial instruments and mark-to-market	228,068	4,570	228,068	4,570
Financial Charges from Customers	(78,220)	(87,593)	(78,222)	(87,593)
Provision for Consent Decree (TAC), Knowledge Retention Program (KRP) and Incentivized Dismissal Program (IDP) and Voluntary Dismissal Program (VDP)	69,893	(295,866)	69,893	(295,866)
Equity Accounting	(12,112)	(12,567)	(8,311)	(11,348)
Interest and inflation adjustment (PPP)	122,675	159,821	122,675	159,821
Municipal transfers	175,359	120,900	175,452	120,900
Pension plan obligations	41,154	65,272	41,154	65,272
Deferred PIS and Cofins on financial asset of the concession	31,680	62,885	31,680	62,885
Financial asset of the concession - restatement	(342,488)	(420,229)	(342,488)	(420,229)
Other adjustments	56,089	(12,038)	73,023	(9,040)
	4,176,180	3,199,718	4,198,490	3,206,487
Changes in assets
Trade receivables	(184,274)	(148,653)	(184,664)	(152,222)
Related-party balances and transactions	35,173	70,291	35,204	70,287
Inventories	(99,009)	(50,672)	(99,022)	(50,672)
Taxes Recoverable	(128,326)	(21,571)	(128,743)	(21,577)
Escrow Deposits	(8,968)	41,907	(8,968)	41,907
Other assets	(18,474)	35,595	83,783	33,147

Changes in liabilities
Trade payables and contractors	(97,729)	(749,490)	(58,955)	(746,743)
Services payable	(344,550)	423,096	(346,126)	422,455
Labor and social obligations	(370,777)	(12,261)	(370,777)	(12,261)
Taxes and contributions payable	(366,900)	(305,290)	(366,970)	(304,152)
Deferred PIS/Cofins	(12,343)	(24,012)	(12,343)	(24,012)
Provisions	(14,922)	(55,701)	(14,922)	(55,701)
Pension plan obligations	(62,453)	(57,008)	(62,453)	(57,008)
Other liabilities	43,578	(119,858)	(73,955)	(119,731)
Cash generated from operations	2,546,206	2,226,091	2,589,579	2,230,204

Interest Paid	(1,268,116)	(760,885)	(1,210,954)	(760,885)

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statements of Cash Flows for the

Periods ended March 31, 2026 and 2025

In thousands of reais, unless otherwise stated

Income and social contribution taxes paid	(615,674)	(366,447)	(616,987)	(368,799)

Net cash generated from operating activities	662,416	1,098,759	761,638	1,100,520

Cash flows from financing activities
Acquisition of contract assets, intangible assets and property, plant and equipment	(5,016,963)	(1,548,895)	(5,056,694)	(1,549,922)
Restricted cash	(7,996)	(1,395)	(7,996)	(1,395)
Financial investments - Investment	(18,889,693)	(4,352,868)	(18,982,625)	(4,360,677)
Financial investments - Redemption	11,564,384	4,432,087	11,567,987	4,437,855
Dividends received	8,156	-	8,156	-
Acquisition of subsidiary, net of cash acquired (consolidated)	(682,643)	-	(302,293)	-
Net cash used in investment activities	(13,024,755)	(1,471,071)	(12,773,465)	(1,474,139)

Cash flows from financing activities
Borrowings and financing
Funding	13,873,101	3,636,828	13,873,101	3,636,828
Amortization	(1,550,259)	(1,126,479)	(1,550,259)	(1,126,479)
Acquisition of non-controlling interests	(739,343)	—	(739,343)	—
Public-Private Partnership - PPP	(123,390)	(136,484)	(123,390)	(136,484)
Derivative financial instruments - paid	(512,568)	(42,699)	(571,268)	(42,699)
Net cash generated from (used in) financing activities	10,947,541	2,331,166	10,888,841	2,331,166

Increase / (decrease) in cash and cash equivalents in the period	(1,414,798)	1,958,854	(1,122,986)	1,957,547

Represented by:
Cash and cash equivalents at the beginning of the period	4,569,998	1,681,204	4,663,226	1,682,606
Cash and cash equivalents at the end of the period	3,155,200	3,640,058	3,540,240	3,640,153
Increase / (decrease) in cash and cash equivalents in the period	(1,414,798)	1,958,854	(1,122,986)	1,957,547

Companhia de Saneamento Básico do Estado de São Paulo - SABESP

Statements of Value Added for the

Periods ended March 31, 2026 and 2025

In thousands of reais

		Individual		Consolidated
	Note	March 31, 2026	March 31, 2025	March 31, 2026	March 31, 2025
Revenue
Sanitation services (includes FAUSP)	31	6,739,003	6,329,839	6,406,603	6,339,411
Construction		3,632,709	2,587,970	3,633,311	2,588,996
Other revenue		6,558	23,569	7,531	23,569
Allowance for doubtful accounts	10 (c)	(53,493)	(136,407)	(53,602)	(136,699)
		10,324,777	8,804,971	10,336,331	8,815,277
Inputs purchased from third parties
Operating and construction costs		(4,646,824)	(3,542,731)	(4,650,069)	(3,532,660)
Materials, electricity, outsourced services, and others		(218,263)	(365,417)	(220,309)	(366,792)
Other operating expenses	34	(24,855)	(4,165)	(24,852)	(4,163)
		(4,889,942)	(3,912,313)	(4,895,230)	(3,903,615)

Gross value added		5,434,835	4,892,658	5,441,101	4,911,662

Retentions
Depreciation and amortization	32	(696,237)	(582,326)	(697,472)	(583,560)

Wealth created by the Company		4,738,598	4,310,332	4,743,629	4,328,102

Wealth received in transfer
Equity Accounting	12	12,112	12,567	8,311	11,348
Financial income		1,217,179	362,550	1,373,599	364,084
		1,229,291	375,117	1,381,910	375,432

Total value added to distribute		5,967,889	4,685,449	6,125,539	4,703,534

Value added distribution

Personnel
Direct Compensation		418,426	385,655	418,508	385,940
Benefits		90,245	166,634	90,272	166,634
Guarantee Fund for Length of Service (FGTS)		37,830	77,596	37,837	77,596
		546,501	629,885	546,617	630,170
Taxes, fees, and contributions
Federal		1,136,887	1,382,348	1,138,767	1,385,464
State		53,702	49,596	53,825	49,628
Municipal		25,956	17,492	25,956	17,492
		1,216,545	1,449,436	1,218,548	1,452,584
Value distributed to providers of capital
Interest, exchange rate changes and inflation adjustments		2,446,479	1,113,502	2,601,995	1,128,153
Rentals		9,333	10,534	9,348	10,535
		2,455,812	1,124,036	2,611,343	1,138,688
Value distributed to shareholders
Retained earnings		1,749,031	1,482,092	1,749,031	1,482,092
		1,749,031	1,482,092	1,749,031	1,482,092

Value added distributed		5,967,889	4,685,449	6,125,539	4,703,534

May 7, 2026

1Q26 adjusted EPS³ of R$0.44 versus R$0.34 in 1Q25

R$3.7 bn Capex in 1Q26 aimed at universal access, +31% y/y

SÃO PAULO, SP – Sabesp (SBSP3) reported adjusted earnings of R$0.44 per share in the 1Q26, compared to R$0.34 per share in the same period of the previous year.

“We entered 2026 maintaining strong execution momentum. In 1Q26, investments totaled R$3.7 billion, a 31% increase versus 1Q25, supporting operational expansion and service quality improvements. Adjusted EBITDA reached R$3.8 billion (+26% y/y) and Adjusted Net Income¹ totaled R$1.6 billion (+32% y/y), reinforcing the consistency of our operating performance and financial discipline,” said Daniel Szlak, CFO of Sabesp.

“Beyond the financial results, our priority continues to be delivering tangible advances in sanitation coverage and service standards. We are consistently outperforming the U-Factor benchmarks for the 2024–2026 cycle, with targets at 87% in water supply, 77% in sewage collection, and 71% in sewage treatment, reflecting sustained operational improvements rather than one-off gains.

Our investment program is driving broad social and economic impact by expanding access to essential services while strengthening communities through large-scale infrastructure execution, positioning the Company to sustain and scale these outcomes throughout 2026,” said Carlos Piani, CEO of Sabesp.

Consolidated Results

For the quarter ended March 31, 2026, Sabesp reported adjusted earnings per share³ of R$0.44 compared to R$0.34 recorded in the same period of the previous year. Performance was driven by volume growth resulting from new connections (U-Factor targets fully attained), tariff gains and better collection, partially offset by the change in customer mix, with the expansion of consumers with access to subsidized rates².

The quarter sustained strong efficiency gains, driven by reductions in general and administrative expenses, headcount reduction, power optimization with shifts to the free market, and better collection rates. As a result, Adjusted EBITDA increased by 26%, reaching R$3.8 billion in 1Q26, while Adjusted Net Income grew by 32%, totaling R$1.6 billion

Sabesp invested R$3.7 bn in 1Q26, a 31% increase over the same period of the previous year, focusing on expansion projects directly aimed at meeting universalization targets.

Earnings Conference Call

Will be held on May 8, 2026, at 10:00 AM (Brasília time). Access link is available at the Company’s Investor Relations website. The presentation has been made available at the same website. An audio recording of the call will be posted at the same website.

Excluding the update of the financial asset (indemnification)

Covered from July/25 onward by the amendment signed between Sabesp and URAE-1 (https://semil.sp.gov.br/urae1/wpcontent/uploads/sites/26/2025/08/2-Termo_Aditivo_Assinado_URAE1_ARSESP_SABESP.pdf)

Considers the stock split in the proportion 1:5 as approved in the EGM of April 28, 2026

REPORTED INCOME STATEMENT (CONSOLIDATED)

R$ mn

		1Q26	1Q25	Var. (R$)	%
	Revenue from Operations	6,366	6,120	247	4.0
	FAUSP	40	(200)	240	(120.0)
	Financial Asset	342	420	(78)	(18.5)
	Sales Tax	(418)	(502)	85	(16.9)
(=)	Net Sanitation Revenue	6,332	5,837	494	8.5
	Construction revenues	3,633	2,589	1,044	40.3
(=)	Net Revenue	9,965	8,426	1,538	18.3
	Construction costs	(3,633)	(2,589)	(1,044)	40.3
	Operating Costs and expenses	(2,241)	(2,439)	199	(8.1)
	Other operating income/(expense), net	(19)	18	(37)	(203.9)
	Minority Interest	8	11	(3)	(26.8)
(=)	EBITDA	4,080	3,427	653	19.1
(%)	Margin	41%	41%	-	0.3
	Depreciation and Amortization	(697)	(584)	(114)	19.5
(=)	EBIT	3,383	2,844	539	19.0
	Net Financial result	(1,025)	(593)	(432)	72.9
(=)	EBT	2,358	2,251	107	4.7
	Income tax	(609)	(769)	160	(20.8)
(=)	Net income	1,749	1,482	267	18.0
(%)	Margin	18%	18%	-	(0.0)
	EPS (R$)	0.50	0.43	-	-

ADJUSTED INCOME STATEMENT (CONSOLIDATED)

1Q26

R$ mn

		1Q26	Adjustments			1Q26 Adjusted	1Q25 Adjusted	Var. (R$)	%
		1Q26	Financial Asset	Construction	Non-Recurring	1Q26 Adjusted	1Q25 Adjusted	Var. (R$)	%
	Revenue from Operations	6,366	-	-	-	6,366	6,120	247	4.0
	FAUSP	40	-	-	-	40	(200)	240	(120.0)
	Financial Asset	342	342	-	-	-	-	-	-
	Sales Tax	(418)	(32)	-	-	(386)	(491)	105	(21.5)
(=)	Net Sanitation Revenue	6,332	311	-	-	6,021	5,428	593	10.9
	Construction revenues	3,633	-	3,633	-	-	-	-	-
(=)	Net Revenue	9,965	311	3,633	-	6,021	5,428	593	10.9
	Construction costs	(3,633)	-	(3,633)	-	-	-	-	-
	Operating Costs and expenses	(2,241)	-	-	-	(2,241)	(2,449)	209	(8.5)
	Other operating income/(expense), net	(19)	-	-	(16)	(3)	18	(21)	(115.6)
	Minority Interest	8	-	-	-	8	11	(3)	(26.8)
(=)	EBITDA	4,080	311	-	(16)	3,786	3,008	778	25.9
(%)	Margin	41%	-	-	-	63%	55%	-	7.5
	Depreciation and Amortization	(697)	-	-	-	(697)	(584)	(114)	19.5
(=)	EBIT	3,383	311	-	(16)	3,088	2,425	664	27.4
	Net Financial result	(1,025)	-	-	-	(1,025)	(638)	(387)	60.7
(=)	EBT	2,358	311	-	(16)	2,063	1,787	276	15.5
	Income tax	(609)	(106)	(0)	5	(508)	(611)	103	(16.8)
(=)	Net income	1,749	205	-	(11)	1,554	1,176	379	32.2
(%)	Margin	18%	-	-	-	26%	22%	-	4.2
	EPS (R$)*	0.50	-	-	-	0.44	0.34	-	-

*Balance adjusted by construction revenue/cost

Non-recurring effects on 1Q26 EBITDA: R$ (16) mn related to M&A expenses.

Due to the migration to SAP S/4HANA, a temporary cutover reduced March 2026 billing by two days. This effect negatively impacted billing volumes and revenues in the period and is expected to be recovered over the subsequent months.

In 1Q26, total water production reached 778 million cubic meters, 4.6% lower year-over-year compared to 1Q25. This decline reflects a milder summer, with average temperatures 3.3 °C lower than last year, as well as the application of SP Aguas operational rule of the night pressure management implemented for approximately 10 hours per day to enhance the system resilience.

ADJUSTED NET REVENUE

Adjusted net revenue from sanitation services, considering FAUSP and taxes, totaled R$ 6,021 mn in 1Q26, an increase of +10.9% vs 1Q25. The main factors that impacted revenue in the period were:

+11.9% in net price: +9.1% tariff phase-in and +2.8% due to commercial initiatives (large clients and revenue assurance);

+2.4% in volume: New units +2.9%, partially offset by lower average temperature (3.3)ºC and lower reservoir levels, affecting consumption per capita negatively;

(3.4)% in mix: Growth in units with access to subsidized rates;

CONSUMPTION BY CATEGORY

	Billed Volume (millions of m³)			Average Rate (R$/m³)
Category	1Q26	1Q25	%	1Q26	1Q25	%
Residential	949	939	1.1	4.31	4.21	2.3
Commercial	95	98	(3.3)	15.46	15.04	2.8
Industrial	17	18	(8.6)	20.82	19.06	9.2
Total Retail	1,061	1,055	0.5	5.57	5.47	1.7
Wholesale	13	13	(3.0)	3.02	2.76	9.1
Others¹	23	30	(24.6)	21.62	16.39	31.9
Total	1,096	1,098	(0.2)	5.87	5.74	2.2

(1)

Others are composed of Public, Own Building, and Mauá (BRK).

Wholesale and Others in 1Q25 was adjusted to incorporate the amount related to Olímpia.

Number of connections in thousands¹	1Q26	1Q25	Var.	%
Water¹	9,468	9,491	(22.5)	(0.2)
Sewage¹	8,211	8,219	(7.8)	(0.1)

(1) Active and registered connections, average at the end of the period

Not audited by external auditors

COST AND EXPENSE

In 1Q26, OPEX decreased by 7.7% compared to 1Q25, representing a reduction of R$ 188 mn. This performance was mainly driven by: (i) R$ 170 mn in savings in personnel expenses, reflecting an 13% headcount reduction, workforce mix and labor benefits streamlining; (ii) energy cost savings, primarily due to the migration from the regulated market to the free market, reaching 86% (+12.6pp y/y). These effects were partially offset by higher general expenses related to municipal funds (FMSAI), reflecting higher revenues compared to last year.

R$ mn

	1Q26 Adjusted	1Q25 Adjusted	Var. (R$)	%
Personnel	(485)	(655)	170	(25.9)
General supplies	(122)	(70)	(53)	75.6
Treatment supplies	(163)	(158)	(5)	2.9
Services	(706)	(696)	(10)	1.4
Power	(384)	(440)	56	(12.7)
General expenses	(290)	(264)	(26)	9.8
Tax expenses	(37)	(21)	(17)	81.5
Allowance for doubtful accounts	(54)	(147)	93	(63.5)
Other revenues and expenses¹	(3)	18	(21)	(115.6)
Costs and Expenses	(2,243)	(2,431)	188	(7.7)
Depreciation and Amortization	(697)	(584)	(114)	19.5
Costs, Expenses, Depreciation and Amortization	(2,941)	(3,015)	74	(2.4)

PERSONNEL

Sabesp ended 1Q26 with 8,927 employees, 8% reduction vs the same period of the previous year, and a 13% reduction

when considering the average number of employees.

Number of employees	1Q26	1Q25	Var. (Qty.)	%
Employees at the end of each period	8,927	9,700	(773)	(8.0)
Employees - simple average	8,814	10,089	(1,275)	(12.6)

CAPITAL EXPENDITURSES

In 1Q26, CapEx totaled R$ 3,728 mn, an increase of 30.8% compared to the same period of the previous year.

R$ mn

	1Q26	1Q25	Var. (R$)	%
Water	1,243	615	627	102.0
Sewage	2,485	2,236	249	11.2
Total	3,728	2,851	877	30.8

In 1Q25 minority interest was considered in Other Revenues and Expenses line. This was changed in 2Q25. 1Q25 was adjusted to reflect the same criteria.

BALANCE SHEET (CONSOLIDATED)

ASSETS	1Q26	4Q25
Current assets
Cash and Equivalents	3,540,240	4,663,226
ST investments	15,641,914	7,707,745
Trade receivables	4,571,688	4,413,449
Related parties	276,096	276,388
Inventories	125,780	22,061
Restricted cash	17,864	9,575
Taxes	1,540,437	1,295,310
Held for sale	48,150	26,864
Other assets	187,137	141,892
Total Current assets	25,949,306	18,556,510

Fixed and LT assets
Trade receivables	367,159	258,544
Related parties	852,234	862,782
Legal deposits	190,446	120,021
Deferred income tax and social contribution	41,513	-
Taxes to be recovered	267,575	-
Other assets	32,502	33,509
PP&E	243,146	254,358
Investments	328,066	49,933
Non-operating Property	14,268,245	11,018,516
Contract asset (Construction in progress)	22,321,254	21,665,330
Financial asset (Indemnity)	50,732,495	50,492,473
Intangible	1,124,763	890,791
Total noncurrent assets	90,769,398	85,646,257
Total Assets	116,718,704	104,202,767

LIABILITIES AND EQUITY	1Q26	4Q25
Current liabilities
Trade payables	872,111	2,400,046
Services payable	2,601,742	2,772,416
ST Debt	4,872,680	5,092,816
Labor	435,732	699,629
Tax	303,085	615,592
Sales Tax	81,432	89,049
Dividends and IoC	2,063,503	2,059,850
Legal Accruals	1,380,446	1,370,013
Public-Private Partnership	473,049	469,687
Derivatives	1,484,755	661,421
Performance Agreements	125,766	120,776
Others	228,068	201,619
Total Current liabilities	14,922,369	16,552,914

Noncurrent Liabilities
LT Debt	46,769,945	35,049,531
Tax	3,076,274	3,129,908
Salex Tax	1,218,870	1,191,916
Legal Accruals	711,943	533,399
Pension	2,407,944	2,140,161
Public-Private Partnership	2,851,931	2,856,008
Performance Contracts	3,543	6,151
Contract liabilities	626,985	-
Others	304,875	341,655
Total Noncurrent Liabilities	57,972,310	45,248,729
Total Liabilities	72,894,679	61,801,643

Equity
Capital stock	21,379,216	21,210,000
Capital reserves	65,843	30,219
Earnings reserves	21,348,996	21,518,212
Treasury Shares	(475,385)	(475,385)
Other Comprehensive Income	117,652	118,078
Retained Earnings/Accumulated Losses	1,264,634	-
Total Equity - Controlling Shareholders	43,700,956	42,401,124
Interest of Non- Controlling Shareholders	123,069	-
Total Equity	43,824,025	42,401,124
Total Equity and Liabilities	116,718,704	104,202,767

STATEMENT OF CASH FLOWS (CONSOLIDATED)

R$ ‘000	1Q26	1Q25
Cash flows from operations	4,198,490	3,206,487
Earnings before Tax	2,357,565	2,250,926
Adjustments on net income:
Depreciation and amortization	697,472	583,560
Fixed Assets write-off	1,587	934
Allowance for doubtful accounts	53,602	136,699
Accruals and inflation over accruals	29,833	158,411
Interest owed	1,292,903	646,698
Interest and inflation adjustments, net	(547,396)	(160,113)
Derivatives	228,068	4,570
Financial Charges from Customers	(78,222)	(87,593)
Voluntary dismissal plans	69,893	(295,866)
Equity pick-up	(8,311)	(11,348)
PPP Interest and inflation	122,675	159,821
SP City Transfers	175,452	120,900
Pension	41,154	65,272
Deferred Sales Tax on financial assets (indemnity)	31,680	62,885
Update of financial asset (indemnity)	(342,488)	(420,229)
Others	73,023	(9,040)
	4,198,490	3,206,487
Changes in assets
Trade receivables	(184,664)	(152,222)
Related parties	35,204	70,287
Inventory	(99,022)	(50,672)
Tax	(128,743)	(21,577)
Escrow	(8,968)	41,907
Others	83,783	33,147

Changes in liabilities
Trade payables	(58,955)	(746,743)
Services payables	(346,126)	422,455
Labor	(370,777)	(12,261)
Income Tax	(366,970)	(304,152)
Sales Tax	(12,343)	(24,012)
Accruals	(14,922)	(55,701)
Pension	(62,453)	(57,008)
Others	(73,955)	(119,731)
Cash from operations	2,589,579	2,230,204
Interest paid	(1,210,954)	(760,885)
Income tax	(616,987)	(368,799)
Free cashflow from operations	761,638	1,100,520


Cash-flow from investments
Contract, intangible assets and PP&E	(5,056,694)	(1,549,922)
Restricted Cash	(7,996)	(1,395)
Financial investments – Investment	(18,982,625)	(4,360,677)
Financial Investments – Withdrawal	11,567,987	4,437,855
Investment	8,156	-
Equity redemption/(injection) in subsidiaries	(302,293)	-
Free cashflow from investments	(12,773,465)	(1,474,139)

Cash flow from financing activity
Borrowings
Debt issuance	13,873,101	3,636,828
Amortization	(1,550,259)	(1,126,479)
Acquisition of non-controlling interests	(739,343)	-
PPP	(123,390)	(136,484)
Derivatives	(571,268)	(42,699)
Free cashflow from financing activities	10,888,841	2,331,166

Increase / (decrease) in cash and cash equivalents in the period	(1,122,986)	1,957,547

Represented by:
Cash and equivalents BoP	4,663,226	1,682,606
Cash and equivalents EoP	3,540,240	3,640,153
Increase / (decrease) in cash and cash equivalents in the period	(1,122,986)	1,957,547

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

Operations

Companhia de Saneamento Básico do Estado de São Paulo (“SABESP”) is a publicly-held corporation headquartered in the municipality of São Paulo, at Rua Costa Carvalho, 300, CEP 05429-900. SABESP and its direct and indirect subsidiaries, individually or collectively (the “Company”), is engaged in the provision of basic and environmental sanitation services in São Paulo State, and supplies treated water and sewage services on a wholesale basis. SABESP may perform activities in other states and countries and can operate in drainage, urban cleaning, solid waste handling, and energy markets.

Since January 2026, following the acquisition of Empresa Metropolitana de Águas e Energia (“EMAE”), the Company has also begun operating in the planning, construction, operation, and maintenance of energy generation systems, as well as in the commercialization of electric power.

The Company's shares have been listed on the Novo Mercado segment of B3 under ticker SBSP3 since April 2002 and on the New York Stock Exchange (“NYSE”) as Level III American Depositary Receipts (“ADRs”), under ticker SBS, since May 2002.

Approvals

The quarterly financial information was approved by the Board of Directors on May 7, 2026.

2 Basis of preparation and presentation of the quarterly information

The quarterly information as of March 31 ,2026, was prepared based on the provisions of CPC 21 (R1) – Interim Financial Statements and the international standard IAS 34 – Interim Financial Reporting, issued by the International Accounting Standards Board (IASB), applicable to the preparation of Quarterly Information (ITR), and presented according to the rules issued by the CVM. Accordingly, this quarterly information takes into consideration the Circular Letter CVM/SNC/SEP 003 of April 28, 2011, which allows the entities to present selected notes to the financial statements in cases of redundant information already disclosed in the Annual Financial Statements. The quarterly information as of March 31, 2026, shall be read jointly with the Annual Financial Statements as of December 31, 2025, issued on March 16, 2026, prepared under the International Financial Reporting Standards (IFRS), issued by the International Accounting Standards Board (IASB), and the accounting practices adopted in Brazil, which observe the pronouncements issued by the Brazilian Accounting Pronouncements Committee (CPC). Therefore, the explanatory notes of this quarterly information are not presented or are not at the same level of detail and/or with the same reference as the notes included in the Annual Financial Statements (according to numerical references):

Summary of material accounting policy information (Note 3);

ii.

Changes in accounting practices and disclosures (Note 4);

iii.

Risk management - Financial instruments (Note 5.4);

iv.

Significant accounting estimates and judgments (Note 6);

Balances and transactions with related parties (Note 11);

vi.

Investments (Note 12);

vii.

Intangible Assets (Note 15);

viii.

Borrowings and financing (Note 17);

ix.

Provisions (Note 23);

Pension plan obligations (Note 25);

xi.

Equity (Note 27);

All material information related to the quarterly information, and this information alone, is being disclosed and corresponds to the information used by the Company’s Management in its administration.

The Company prepared the financial statements on a going concern basis.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

The amounts disclosed in the Notes are presented in thousands of reais, unless otherwise stated.

3 Summary of material accounting policy information

The material accounting policy information used in the preparation of the quarterly information as of March 31, 2026, is consistent with that used to prepare the Annual Financial Statements for the year ended December 31, 2025. As a result of the business combination completed in the current quarter (Note 4), the following accounting policies have become applicable to the Company:

Business combination

Business combinations are accounted for using the acquisition method. The cost of an acquisition is measured by the sum of the consideration paid, which is evaluated based on the fair value on the acquisition date, and the value of any non-controlling interests in the acquiree. For each business combination, the acquirer must measure the non-controlling interest in the acquiree at fair value or based on its interest in the net assets identified in the acquiree. Costs directly attributable to the acquisition are accounted for as expense when incurred.

The Company determines that it has acquired a business when the acquired set of activities and assets includes, at least, an input of resources and a substantive process that together contribute significantly to the ability to generate output of resources. The process acquired is considered substantive if it is essential to the ability to develop or convert the input of resources acquired into outputs of resources (and the inputs of resources acquired include both the organized workforce with the skills, knowledge or experience necessary to perform this process); or is critical to the ability to continue producing outputs and is considered unique or scarce, or cannot be replaced without significant cost, effort or delay in the ability to continue producing outputs of resources.

Any contingent consideration to be paid by the acquirer will be recognized at fair value on the acquisition date. Subsequent changes in the fair value of the contingent consideration deemed as an asset or as a liability shall be recognized in accordance with CPC 48 / IFRS 9 in the profit or loss statement.

Initially, goodwill is measured as the excess of the consideration paid in relation to the net assets acquired (identifiable assets acquired, net, and liabilities assumed). If the consideration is less than the fair value of the net assets acquired, the difference shall be recognized as gain in the profit or loss statement.

After initial recognition, goodwill is measured at cost, less any accumulated impairment losses. For impairment testing purposes, the goodwill acquired in a business combination is, as of the acquisition date, allocated to each of the Company's cash-generating units that are expected to benefit from the synergies of the combination, regardless of whether other assets or liabilities of the acquiree are attributed to those units.

When a goodwill is part of a cash-generating unit and a portion of that unit is disposed of, the goodwill associated with the portion disposed of must be included in the cost of the operation when determining the gain or loss on disposal. The goodwill disposed of in these circumstances is calculated based on the proportional values of the portion disposed of in relation to the cash-generating unit held.

4 Business combination and acquisition of non-controlling interests

Empresa Metropolitana de Águas e Energia S.A. (“EMAE”)

On January 21, 2026, the Company acquired 29.9% of the total capital and 74.9% of the voting capital of EMAE, representing 11,009,550 (eleven million, nine thousand, five hundred and fifty) common shares of the company that focuses on the planning, construction, operation and maintenance of electricity generation systems, as well as their commercialization, operating under a concession regime. The transaction was motivated by a combination of factors:

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

•

Advanced water integration ensuring security of supply

•

Operational synergy between water and energy

•

Use of strategic window

•

Technical and regulatory feasibility

This holistic approach reflects SABESP's strategy to strengthen its position as an essential services company in a context of climate challenges, growing demand and the need for better operational efficiency.

Assets acquired and liabilities assumed

In accordance with the provisions of CPC 15/IFRS 3, although the acquisition of control and, consequently, the business combination occurred on January 21, 2026, the Company considered the beginning of the acquisition month, i.e., January 1, 2026, for purposes of measuring the acquired assets and assumed liabilities, the Company adopted the beginning of the acquisition month, January 1, 2026, as the effective acquisition date, applying a three-month reporting lag as permitted by the applicable accounting standards. Based on this date, no results of the acquire are included in the consolidated financial statements. The fair value of EMAE’s identifiable assets and liabilities as of that date is presented below:

	Fair value recognized in the acquisition		Fair value recognized in the acquisition
Assets		Liabilities
Cash and cash equivalents	380,350	Trade payables and contractors	28,797
Trade receivables	46,030	Borrowings and financing	448
Taxes Recoverable	371,325	Labor and social obligations	28,237
Other assets	136,895	Taxes and contributions payable	9,297
Escrow Deposits	61,457	Dividends and interest on capital payable	10,325
Deferred income and social contribution taxes	41,513	Other liabilities	29,603
Investment properties	316,589	Borrowings and financing	3,533
Financial asset	195,375	Provisions	174,066
Intangible assets	19,253	Pension plan obligations	271,781
Property, plant, and equipment	209,108	Contract liabilities	626,985
Total Assets	1,777,895	Total liabilities	1,183,072

Total net identifiable assets at fair value	594,823
Non-controlling interests measured at the proportionate share method	(417,090)
Goodwill/Identifiable asset	504,910
Total consideration	682,643

These effects are preliminary, as at the date of this disclosure the procedures for the purchase price allocation are still in progress, primarily related to the inspection of the acquired fixed assets, among other analyses. The final allocation of EMAE’s purchase price depends on valuations and other studies that have not yet been completed, as well as on the issuance of the final appraisal report to be prepared by an independent specialized firm.

The goodwill/identifiable asset amounting to R$ 504,910 recognized upon the acquisition arises substantially from expected synergies associated with the business combination. This amount is provisional and subject to the completion of the

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

purchase price allocation (PPA) process, and may be adjusted as the fair value assessments of the identifiable assets acquired and liabilities assumed are finalized.

The Company adopted, as an accounting policy, the measurement and initial recognition of the non-controlling interest using the proportional interest share method.

The total consideration given was settled exclusively in cash, so that there are no clauses providing for supplementary payment by means of contingent payment, put/call option, issue or transfer of shares, assumption of liabilities or transfer of other assets to acquire the interest.

Analysis of the cash flow from acquisition
Total consideration paid	(682,643)
Net cash acquired from the subsidiary (included in cash flows from investment activities)	380,350
Net cash flow from acquisition	(302,293)

The disclosure of pro forma net operating revenue and net income was not presented, as the acquisition balance sheet already reflects the effects as of the beginning of the fiscal year.

Transaction costs in the amount of R$ 16,000 were recognized in the profit or loss statement as general and administrative expenses.

Acquisition of additional interest in EMAE

After obtaining control, the Company acquired additional non-controlling interests, increasing its shareholding to 79.31%:

•

On January 28, 2026, the Company acquired interest representing 40.21% from Eletrobrás for the amount of R$ 567,705.

•

On March 12, 2026, the Company acquired interest representing 9.22% from Oceania for the amount of R$ 171,638.

The carrying amount of the net assets as of the acquisition date amounted to R$ 294,021. The breakdown of the additional interest acquired is shown below:

Consideration paid to non-controlling shareholders	739,343
Earn-out	39,075
Carrying value of the additional interest acquired	(295,021)
Difference recognized in retained earnings	484,397

5 Risk management

5.1 Financial risk management

Financial risk factors

The Company's activities are affected by the Brazilian economic scenario, making it exposed to market risk (exchange rate and interest rate), credit risk, and liquidity risk. Financial risk management focuses on the unpredictability of financial markets and seeks to minimize potential adverse effects on financial performance. There were no changes in risk measurement policies, processes, and methods compared to the previous year.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

(a) Market risk

Foreign currency risk

It is the risk that the fair value of the future cash flows of a financial instrument will fluctuate due to variations in exchange rates. The Company's exposure to the risk of changes in exchange rates refers mainly to its financing activities, since the Company has foreign currency-denominated liabilities arising from long-term financing, in development institutions in US Dollar, Euro and Yen.

The management of currency exposure considers several current and projected economic factors, besides market conditions.

This risk arises from the possibility that the Company may incur losses due to exchange rate fluctuations that would impact liability balances of foreign currency-denominated borrowings and financing and related finance costs. The Company manages its foreign exchange risk through hedging transactions since 2024 and negotiates the terms of the derivatives in order to comply with the terms of the exposure hedged under Note 19.

Part of the total financial debt in the amount of R$ 17,879,630 as of March 31, 2026 (R$ 10,632,252 as of December 31, 2025), is indexed to the U.S. dollar, Euro and Yen. The exposure to currency risk is as follows:

	Individual		Consolidated		Individual		Consolidated
	March 31, 2026		March 31, 2025		December 31, 2025		December 31, 2025
	Foreign currency (in thousands)	R$	Foreign currency (in thousands)	R$	Foreign currency (in thousands)	R$	Foreign currency (in thousands)	R$
Borrowings and financing – US$	2,247,849	11,732,423	2,747,849	14,342,123	750,889	4,131,691	1,250,889	6,882,891
Borrowings and financing – Yen	60,495,723	1,984,865	60,495,723	1,984,865	62,496,777	2,196,137	62,496,777	2,196,137
Borrowings and financing – EURO	220,000	1,322,574	220,000	1,322,574	220,000	1,423,224	220,000	1,423,224
Interest and charges from borrowings and financing – US$		143,656		160,878		44,876		110,009
Interest and charges from borrowings and financing – Yen		9,020		9,020		8,818		8,818
Interest and charges from borrowings and financing – EURO		24,254		24,254		12,033		12,033
Fair value adjustment - US$		284,023		267,284		47,666		143,636
Fair value adjustment - Yen		(99,427)		(99,427)		(67,281)		(67,281)
Fair value adjustment - EURO		28,329		28,329		34,631		34,631
Total Exposure		15,429,717		18,039,900		7,831,795		10,744,098
Borrowing cost – US$		(170,968)		(129,303)		(61,401)		(80,063)
Borrowing cost – Yen		(12,119)		(12,119)		(12,389)		(12,389)
Borrowing costs – EURO		(18,848)		(18,848)		(19,394)		(19,394)
Total foreign currency-denominated borrowings (Note 17)		15,227,782		17,879,630		7,738,611		10,632,252

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

The table below shows the prices and exchange rate changes in the period:

	March 31, 2026	December 31, 2025	Variation
US$	R$ 5.2194	R$ 5.5024	-5.14%
EURO	R$ 6.0117	R$ 6.4692	- 7.07%
Yen	R$ 0.03281	R$ 0.03514	-6.63%

As of March 31, 2026, if the Brazilian real had depreciated or appreciated by 10 percentage points, against the U.S. dollar, Yen and Euro with all other variables held constant, the effects on profit or loss before borrowing costs and taxes, for the three-month period ended March 31, 2026, would have been R$ 1,780,976 (R$ 305,835 for the three-month period ended March 31, 2025), upwards or downwards, excluding the effects of to the hedging instruments (Note 19).

The Company understands that it could comfortably accommodate any devaluation scenario due to derivative financial instruments such as cross-currency swaps already contracted.

Interest rate risk

It is the risk that the fair value of the future cash flows of a financial instrument will fluctuate due to variations in market interest rates. For most transactions, the Company manages the interest rate risk by entering into derivative financial instruments that effectively swap their exposures for liabilities indexed to the CDI.

The table below shows the borrowings and financing subject to different inflation adjustment indices, including the derivative instrument:

Individual			Consolidated
	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025
CDI (i)	45,977,065	33,593,125	43,142,285	30,722,218
TR (ii)	1,604,468	1,629,756	1,604,468	1,629,756
IPCA (iii)	2,972,898	2,924,904	5,582,598	5,582,893
TJLP (iv)	765,263	825,206	765,263	825,206
Interest and charges	1,025,860	1,204,818	1,013,965	1,164,744
Total	52,345,554	40,177,809	52,108,579	39,924,817

(i) CDI - (Certificado de Depósito Interbancário), an interbank deposit certificate

(ii) TR - Benchmark Interest Rate

(iii) IPCA - (Índice Nacional de Preços ao Consumidor Amplo), a consumer price index

(iv) TJLP - (Taxa de Juros a Longo Prazo), a long-term interest rate index

Another risk to which the Company is exposed is the mismatch of inflation adjustment indices of its debts with those of its service revenues and financial assets, adjusted by the IPCA. Tariff adjustments of services provided do not necessarily follow the increases in the adjustments indices of borrowings, financing, and interest rates affecting indebtedness.

As of March 31, 2026, if interest rates on borrowings and financing had been 1 percentage point higher or lower with all other variables held constant, the effects on consolidated profit before taxes for the three-month period ended March 31,

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

2026, would have been R$ 521,086 (R$ 260,714 as of March 31, 2025), upwards or downwards, mainly as a result of lower or higher interest expenses on floating rate borrowings and financing.

The table below shows the sensitivity analysis of the financial instruments, prepared under CPC 40 (R1)/ IFRS 7, to evidence the balances of main financial assets and liabilities, calculated at a rate projected for the twelve-month period after March 31, 2026, or until the final settlement of each contract, whichever occurs first, considering a probable scenario.

The purpose of the sensitivity analysis is to measure the impact of changes in the market on the financial instruments, considering all other variables constant. At the time of settlement, the amounts may be different from those presented, due to the estimates used in the measurement.

The table below considers the impact of the derivative instrument:

	Individual		Consolidated
	March 31, 2026		March 31, 2026
Indicators	Exposure	Probable scenario	Exposure	Probable scenario

Assets
CDI	18,679,922	13.85 %	18,679,922	13.85 %
Financial income		2,587,169		2,587,169

Liabilities
CDI	(45,977,065)	13.85 %	(43,142,285)	13.85 %
Interest to be incurred		(6,367,824)		(5,975,206)
Net exposure – CDI	(27,297,143)	(3,780,654)	(24,462,363)	(3,388,037)

Assets
IPCA	22,125,879	4.00 %	22,125,879	4.00 %
Financial asset of the concession		884,039		884,039

Liabilities
IPCA	(2,972,898)	4.00 %	(5,582,598)	4.00 %
Interest to be incurred		(118,782)		(138,760)
Net exposure – IPCA	19,152,981	765,257	16,543,281	745,280

Liabilities
TR	(1,604,468)	2.02 %	(1,604,468)	2.02 %
Expenses to be incurred		(32,410)		(32,410)

TJLP	(765,263)	9.27 %	(765,263)	9.27 %
Interest to be incurred		(70,958)		(70,958)

Total net expenses to be incurred		(3,118,766)		(2,746,126)

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

(b) Credit risk

Credit risk is related to cash and cash equivalents, financial investments, as well as credit exposures of customers, including accounts receivable, restricted cash, accounts receivable from related parties, and financial asset of the concession. Credit risk exposure to customers is mitigated by sales to a dispersed base, without risk of concentration, while credit risk exposure to cash and investment is mitigated by the Financial Investment Guideline followed by the Company.

The maximum exposure to credit risk as of March 31, 2026, is the carrying amount of instruments classified as cash and cash equivalents, financial investments, restricted cash, trade receivables, accounts receivable from related parties, and financial asset of the concession at the reporting date. See Notes 7, 8, 9, 10, 11, and 15.

Regarding the financial assets held with financial institutions, the credit quality was assessed by reference to external credit ratings (if available) or historical information about the bank’s default rates. For the credit quality of the banks, such as deposits and financial investments, the Company assesses the rating published by three main international agencies (Fitch, Moody's and S&P).

As of March 31, 2026, all investments were made with financial institutions whose rating disclosed by Fitch or Moody's was AAA (bra) or AAA.br.

(c) Liquidity risk

Liquidity is primarily reliant upon cash provided by operating activities and borrowings and financing obtained in the local and international capital markets, as well as the payment of debts. The management of this risk considers the assessment of its liquidity requirements to ensure it has sufficient cash to meet its operating and capital expenditure requirements.

The funds held are invested in interest-bearing current accounts, time deposits, and securities, with instruments with appropriate maturity or liquidity to provide margin as determined by the projections mentioned above.

The table below shows the financial liabilities, by maturity, including the installments of principal and future interest. For agreements with floating interest rates, the interest rates used correspond to the base date of March 31, 2026.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

	Individual
	2027	2028		2029		2030		2031		2032 to 2049	Total
As of March 31, 2026
Liabilities
Borrowings and financing	4,501,267	2,193,706		1,444,652		3,684,405		7,062,707		33,111,696	51,998,433
Interest on borrowings and financing	3,001,422	4,403,293		4,255,760		4,023,578		3,737,555		11,147,599	30,569,207
Trade payables and contractors	842,069	-		-		-		-		-	842,069
Services payable	2,598,708	-		-		-		-		-	2,598,708
Public-Private Partnership - PPP	199,222	239,066		239,066		239,066		239,066		2,169,494	3,324,980
Interest Public-Private Partnership - PPP	192,280	247,101		264,235		281,850		300,082		3,125,341	4,410,889
Total	11,334,968	7,083,166		6,203,713		8,228,899		11,339,410		49,554,130	93,744,286

	Consolidated
	2027	2028		2029		2030		2031		2032 to 2049	Total
As of March 31, 2026
Liabilities
Borrowings and financing	4,490,184	2,194,758		1,445,580		3,685,222		6,715,184		33,111,697	51,642,625
Interest on borrowings and financing	2,949,948	4,300,533		4,151,343		3,920,819		3,634,797		11,147,599	30,105,039
Trade payables and contractors	872,111	-	—	-	—	-	—	-	—	-	872,111
Services payable	2,601,742	-	—	-	—	-	—	-	—	-	2,601,742
Public-Private Partnership - PPP	199,222	239,066		239,066		239,066		239,066		2,169,494	3,324,980
Interest Public-Private Partnership - PPP	192,280	247,101		264,235		281,850		300,082		3,125,341	4,410,889
Total	11,305,487	6,981,458		6,100,224		8,126,957		10,889,129		49,554,131	92,957,386

Cross default

The Company has borrowings and financing agreements including cross-default clauses, i.e., the early maturity of any debt may imply the early maturity of these agreements. The indicators are continuously monitored to avoid the execution of these clauses, and the most restrictive ratios are shown in Note 17 (c).

(d) Derivative financial instruments

Under the Financial Risk Management Policy and the Derivatives Transactions Program, which aim to manage financial risks and mitigate exposure to market variables that impact assets, liabilities, and/or cash flows, the Company enters into hedging instruments, especially for its foreign-currency financing, reducing the effects of undesirable fluctuations from these variables on its transactions.

Criteria and guidelines for financial risk management were established to mitigate imbalances between assets and liabilities that have some sort of indexation exclusively to hedge the Company’s indexed assets and liabilities that present some mismatch, without characterizing financial leverage.

The Company uses risk ratings disclosed by Standard Poor’s (S&P), Moody’s, or Fitch to support and complement the analysis and judgment of banking risk.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

5.2 Capital Management

The Company’s objectives in managing capital are to ensure the Company’s ability to continue increasing investments in infrastructure, provide returns for shareholders and benefits for other stakeholders, and maintain an optimal capital structure to reduce the cost of capital.

Capital is monitored based on the financial leverage ratio, which corresponds to net debt divided by total capital (shareholders and providers of capital). Net debt corresponds to total borrowings and financing less cash and cash equivalents and financial investments. Total capital is calculated as total equity plus net debt, as shown in the statement of financial position.

	Individual		Consolidated
	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025

Total borrowings and financing (Note 17)	51,998,433	40,301,603	51,642,625	40,142,347
(-) Cash and cash equivalents (Note 7)	(3,155,200)	(4,569,998)	(3,540,240)	(4,663,226)
(-) Financial investments (Note 8)	(15,537,279)	(7,693,630)	(15,641,914)	(7,707,745)
Net debt	33,305,954	28,037,975	32,460,471	27,771,376

Total Equity	43,700,956	42,401,124	43,824,025	42,401,124
Total capital (shareholders plus providers of capital)	77,006,910	70,439,099	76,284,496	70,172,500
Leverage ratio	43%	40%	42%	40%

6 Significant accounting estimates and judgments

The preparation of the quarterly information requires Management to disclose judgments (except for those that involve estimates) that have a significant impact on the amounts recognized based on experience and other factors deemed as relevant, which affect the amounts of assets and liabilities and present results that may differ from the actual results.

The Company establishes estimates and assumptions concerning the future, which are reviewed on a timely basis. Such accounting estimates, by definition, may differ from the actual results. The effects arising from the reviews of the accounting estimates are recognized in the period in which the estimates are reviewed.

The Company assessed the main accounting policies that involve judgments, except for those that involve estimates, and concluded that none of them have a significant effect.

The areas that require a higher level of judgment and greater complexity are disclosed below. The assumptions and estimates for each of these areas, when applicable, are presented in the related notes:

Area	Reference
Unbilled revenue	Note 10
Allowance for doubtful accounts	Note 10 (c)

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

Contract assets, intangible assets, and financial assets arising from concession contracts	Notes 13, 14 and 15
Assessment of the recoverable amount of non-financial assets (impairment)	Note 14
Derivative financial instruments	Note 19
Deferred income and social contribution taxes	Note 22
Provisions	Note 23
Pension obligations – Pension plans	Note 26

7 Cash and cash equivalents

	Individual		Consolidated
	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025
Cash and banks	32,758	2,185	37,448	95,411
Cash equivalents	3,122,442	4,567,813	3,502,792	4,567,815
Total	3,155,200	4,569,998	3,540,240	4,663,226

Cash and cash equivalents include cash, bank deposits, and high-liquidity short-term financial investments, mainly represented by daily liquidity CDBs (divided between Banco Itaú, Banco Santander, Banco Bradesco, and Banco do Brasil), whose original maturities or intention of realization are equal to or less than three months, which are convertible into a cash amount and subject to an insignificant risk of change in value.

Of the total balance presented in this item as of March 31, 2026, approximately 99.75% refers to the amounts recorded in Banco Itaú, Banco Santander, Banco Bradesco, and Banco do Brasil.

As of March 31, 2026, the average yield of cash equivalents corresponded to 99.80% of the CDI (99.66% as of December 31, 2025).

8 Financial investments

(a)

Current

The Company has financial investments in CDB, with daily liquidity, which it does not intend to use in the next three months, as shown below:

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

	Individual		Consolidated
	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025
Banco BV	174	169	174	169
Banco Bradesco	5,803,577	1,118,026	5,803,577	1,118,026
Banco Santander S/A	3,792,816	3,699,510	3,792,816	3,699,510
Banco BTG Pactual S/A	2,192,391	2,132,826	2,192,3912	2,132,826
Banco Itaú	3,000,818	-	3,087,092	-
Banco do Brasil S/A	86,732	83,594	105,093	97,709
Brazilian Federal Savings Bank	31,068	30,206	31,068	30,206
XP Investimentos	226,599	215,002	226,599	215,002
Banco Citibank	403,104	414,297	403,104	414,297
Total	15,537,279	7,693,630	15,641,914	7,707,745

As of March 31, 2026, the average yield of the financial investments corresponded to 99.8% of the CDI (99,6% as of December 31, 2025).

9 Restricted cash

Restricted cash balances refer to amounts held by the Company as a result of contractual obligations and specific agreements. As of March 31, 2026, and December 31, 2025, restricted cash operations were R$ 17,864 and R$ 9,575, respectively.

The amounts recorded in 2024 were mainly related to the agreements signed with the São Paulo Municipal Government (“PMSP) and with URAE-1, which provided for the deduction of a portion of the revenue destined to the Municipal Fund for Environmental Sanitation and Infrastructure (“FMSAI) to cover any defaults by public agencies.

These amounts were redeemed throughout 2025, especially between October and November, resulting in the elimination of the balances linked to the agreements with the PMSP.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

10 Trade receivables

(a) Statement of financial position details

	Individual		Consolidated
	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025
Private sector:
General (i) and special customers (ii)	2,536,629	2,431,979	2,587,973	2,436,976
Agreements (iii)	327,030	343,747	327,030	343,747
	2,863,659	2,775,726	2,915,003	2,780,723
Governmental Entities:
Municipal	1,147,549	1,186,815	1,147,218	1,186,531
Federal	2,765	2,670	2,765	2,670
Agreements (iii)	333,396	274,508	333,396	274,508
	1,483,710	1,463,993	1,483,379	1,463,709
Wholesale customers – Municipal governments: (iv)
Mogi das Cruzes	13,898	9,149	13,898	9,149
São Caetano do Sul	34,204	26,884	34,204	26,884
São Caetano do Sul - Agreement	49,173	51,589	49,173	51,589
Total wholesale customers – Municipal governments	97,275	87,622	97,275	87,622

Unbilled supply (v)	1,194,014	1,155,475	1,195,934	1,157,382

Sub-total	5,638,658	5,482,816	5,691,591	5,489,436

Allowance for doubtful accounts	(752,744)	(817,443)	(752,744)	(817,443)
Total	4,885,914	4,665,373	4,938,847	4,671,993

Current	4,518,755	4,406,829	4,571,688	4,413,449
Non-current	367,159	258,544	367,159	258,544
Total	4,885,914	4,665,373	4,938,847	4,671,993

(i)

General customers - residential, and small and mid-sized companies;

(ii)

Special customers – large consumers, industrial and commercial customers, condominiums and special billing customers (fixed demand agreements, industrial waste, wells, among others);

(iii)

Agreements - installment payments of past-due receivables, plus inflation adjustment and interest, according to the agreements;

(iv)

Wholesale basis customers - municipal governments. This balance refers to the sale of treated water to municipalities, which are responsible for distributing to, billing, and charging end consumers.

(v)

Unbilled Supplies: represents revenue incurred, for which the service has been provided but has not yet billed by the end of each period, and is recognized as trade receivables based on monthly estimates.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

(b) The aging of trade receivables is as follows:

	Individual		Consolidated
	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025
Current	3,070,915	2,960,281	3,120,497	2,963,070
Past-due:
Up to 30 days	804,672	747,338	806,380	748,559
From 31 to 60 days	328,971	308,672	329,556	309,579
From 61 to 90 days	208,256	228,767	208,602	229,559
From 91 to 120 days	215,827	242,688	216,053	243,256
From 121 to 180 days	304,777	276,103	305,319	276,446
From 181 to 360 days	209,459	226,600	209,463	226,600
Over 360 days	495,781	492,367	495,721	492,367
Total Past Due	2,567,743	2,522,535	2,571,094	2,526,366
Total	5,638,658	5,482,816	5,691,591	5,489,436

(c) Allowance for doubtful accounts (“ADA”)

	Individual		Consolidated
Changes in assets	January to March 2026	January to March 2025	January to March 2026	January to March 2025
Balance at the beginning of year	817,443	1,248,209	817,443	1,248,209
Recognition/(reversal) of allowance	(27,270)	(30,750)	(27,270)	(30,750)
Recoveries	(37,429)	(34,466)	(37,429)	(34,466)
Balance at the end of year	752,744	1,182,993	752,744	1,182,993

	Individual		Consolidated
Reconciliation of estimated / historical losses in profit or loss - accounts receivable and related parties	January to March 2026	January to March 2025	January to March 2026	January to March 2025

Write-offs	(117,348)	(201,244)	(117,457)	(201,536)
(Losses)/reversal with state entities - related parties	(844)	(379)	(844)	(379)
(Losses)/reversal with the private sector/government entities	27,270	30,750	27,270	30,750
Recoveries	37,429	34,466	37,429	34,466

Amount recorded as expense (Note 32)	(53,493)	(136,407)	(53,602)	(136,699)

The Company does not have customers individually accounting for 10% or more of its total revenues.

(d) Registered warrants

The Company has registered warrants issued as a result of final and unappealable lawsuits for the collection of unpaid water and sewage bills from public entities in the amount of R$ 823,238 thousand (R$ 814,290 thousand as of December 31, 2025). These bills are covered in full by ADA, and the restated amounts of said bills, calculated according to the respective registered warrants, are not recognized due to uncertainties about their realization.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

Accordingly, the reversal of the ADA for the original bills and their restatement are recognized when uncertainties about their realization are mitigated, i.e. when the realizable value is determinable due to the predictability of the commencement of their receipt, without uncertainties or discussions about these amounts or when negotiated with third parties.

Additionally, the Company negotiated registered warrants for overdue bills with the municipalities of Guarulhos, Santo André, and Mauá in previous fiscal years, which are currently suspended as they serve as collateral for the provision of services in these municipalities.

As of March 31, 2026, the Company holds registered warrants recognized in the amount of R$ 823,238 (R$ 814,290 as of December 31, 2025). This amount forms part of the Company’s total trade and other receivables balance of R$ 5,638,658 thousand as of March 31, 2026.

11 Related-party balances and transactions

(a) São Paulo State

(i)

Accounts receivable, interest on equity, revenue, expenses and financial receipts

	Individual		Consolidated
	March 31, 2026	December 31, 2025	March 31, 2026	December 31, 2025

Current
Accounts receivable:
Sanitation services	172,513	163,759	172,588	163,865
Allowance for losses	(43,597)	(42,753)	(43,597)	(42,753)

Reimbursement of additional retirement and pension benefits paid (G0):
Monthly flow	19,251	32,141	19,251	32,141
GESP Agreement – 2015	127,854	123,135	127,854	123,135

Total current	276,021	276,282	276,096	276,388

Non-current
Agreement for the installment payment of sanitation services	1,361	1,361	1,361	1,361

Reimbursement of additional retirement and pension benefits paid (G0):
GESP Agreement – 2015	850,873	861,421	850,873	861,421

Total non-current	852,234	862,782	852,234	862,782

Total receivable	1,128,255	1,139,064	1,128,330	1,139,170

Assets:
Sanitation services	130,277	122,367	130,352	122,473
Reimbursement of additional retirement and pension benefits paid (G0)	997,978	1,016,697	997,978	1,016,697

Total	1,128,255	1,139,064	1,128,330	1,139,170

Liabilities:
Dividends and interest on capital payable	428,681	428,681	428,681	428,681

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

	Individual		Consolidated
	January to March 2026	January to March 2025	January to March 2026	January to March 2025

Revenue from sanitation services	226,234	221,207	226,275	221,240
Payments received from related parties	(207,625)	(208,372)	(207,625)	(208,372)

Reimbursement received referring to Law No. 4.819/1958	(60,512)	(116,628)	(60,512)	(116,628)

The information below refers to the Individual and Consolidated balances and transactions.

(ii)

Disputed amounts

As of March 31, 2026, and December 31, 2025, the disputed amounts between SABESP and the São Paulo State, referring to additional retirement and pension benefits paid (Law No. 4,819/1958), totaled R$ 1,843,857 and R$ 1,808,631, respectively, and an ADA was recognized for the total amount.

(iii)

Actuarial Liability

The Company recognized an actuarial liability corresponding to additional retirement and pension benefits paid to employees, retired employees, and pensioners of the G0 (Note 26). As of March 31, 2026, and December 31, 2025, the amounts corresponding to such actuarial liability were R$ 2,043,866 and R$ 2,140,161, respectively. Of the total paid, the São Paulo State reimburses approximately 50%. For detailed information on additional retirement and pension benefits, see Note 26.

(iv) Agreements with reduced tariffs for Federal, State and Municipal Entities that join the Rational Water Use Program (PURA)

The Company maintains joinder agreements to the PURE Program with public entities operating in the São Paulo State. The purpose of the program is to promote the conscious use of water, granting participating entities a 25% tariff discount, provided that they are in a regular situation of compliance and meet the established goals.

(v) Guarantees

The São Paulo State provides guarantees for some of the Company’s borrowings and financing and does not charge any related fees, see Note 17.

(vi) FEHIDRO

The Company formalized three financing agreements under the State Fund for Water Resources (FEHIDRO). The funds are aimed at the execution of works and sewage services. As of March 31, 2026, the balance of these financings was R$ 1,210, recorded under the “Other” line in borrowings and financing (R$ 938 as of December 31, 2025).

(vii) Privatization

According to Article 7 of Law 9,361/1996, the controlling shareholder will be reimbursed, upon the privatization, the services of independent audit firms, law firms, opinions, or specialized studies necessary for the privatization.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

The amount to be reimbursed by the São Paulo State as of March 31, 2026 and December 31, 2025 was R$ 85,929, recorded under “Other assets”.

(b) Non-operating assets

As of March 31, 2026 and December 31, 2025, the Company had an amount of R$ 3,521 related to land and lent structures under free lease agreements.

(c) SABESPREV

The Company sponsors a defined benefit plan (G1 Plan), which is operated and administered by SABESPREV. The net actuarial commitment recognized until March 31, 2026 was R$ 92,296 (R$ 99,514 as of December 31, 2025). See Note 26.

(d) Key Management Personnel Compensation

The expenses related to the compensation of key management personnel were R$ 28,741 and R$ 8,975 for the years 2025 and 2024, respectively. In addition, the total compensation of the management corresponds to R$ 45,623, which include short-term benefits to management personnel.

Compensation	March 31, 2026	December 31, 2025

Short-term benefits to employees and key management personnel	20,267	39,828
Share-based payments (*)	-	22,618
Total compensation	20,267	62,446

(*) Refers to shares granted during the period. See Note 28 (b).

(e)

Águas de Andradina

As of March 31, 2026, the balance of principal and interest of the loan agreement entered into between the parties was R$ 4,925, recorded under “Other assets” in current assets (R$ 4,718 in current assets as of December 31, 2025), at DI + 3% p.a.

This loan agreement was executed on August 17, 2021 and will be settled with the purchase and sale transaction.

(f) Equatorial S.A.

In July 2024, Equatorial Participações e Investimentos IV S.A., controlled by Equatorial S.A., acquired shares representing 15% (fifteen percent) of the share capital of SABESP. In December 2024, Equatorial S.A. absorbed its subsidiary, becoming the direct holder of the equity interest in SABESP. As of March 31, 2026, the balance of dividends and interest on equity payable was R$ 348,402.

(g) SABESP Luxembourg (“SABESP Lux”)

On August 1, 2025, the Company issued the 36th issue of simple non-convertible unsecured debentures, in the total amount of 2,815,700, with a unit par value of R$ 1, with maturity in 2030 and a yield of IPCA + 9.28% p.a. Of these debentures, 2,765,700 were acquired by SABESP Luxembourg (98.22% of the total securities of this issue). This transaction involved entering into a derivative instrument swapping the yield for CDI (see Note 19).

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

(i) Use of Reservoirs (“EMAE”)

Empresa Metropolitana de Águas e Energia S/A - EMAE intended to receive credit and financial compensation for alleged past and future losses of electricity generation due to water abstraction and compensation for costs already incurred and to be incurred with the operation, maintenance and inspection of Guarapiranga and Billings reservoirs that SABESP uses in its operations.

On October 28, 2016, a Private Instrument of Transaction and Other Covenants were executed with the purpose of definitively settling the disputes, while maintaining SABESP’s authorization to use the aforementioned reservoirs.

As of March 31, 2026, the outstanding balance of the agreement amounted to R$ 10,036 and R$ 109,292 (December 31, 2025: R$ 9,745 and R$ 105,884), recognized under “Other obligations” in the Company’s current and non-current liabilities, respectively.

As a result of the acquisition of EMAE’s control, consummated on January 26, 2026 (see note 4), the balances and obligations arising from this agreement, as transactions between companies that are part of the same economic group, are fully eliminated in the consolidated financial statements.

12 Investments

The following are events in the year that are related to investees:

SABESP Participações S.A.

On January 30, 2026, SABESP Participações S.A., a wholly-owned subsidiary of the Company, approved a capital increase of R$ 15,648, through the issue of 15,648,701 common shares, subscribed and paid in by the Company.

The payment was made through the verification of the equity interests previously held directly by the Company in the affiliates Águas de Andradina S.A. and Águas de Castilho S.A., corresponding to 30% of the capital of each company, valued at book value, based on a report prepared by an independent appraiser, pursuant to Law No. 6,404/76. Of the total, R$ 12,201 refer to the interest in Águas de Andradina S.A. and R$ 3,447 to the interest in Águas de Castilho S.A.

As a result of this transaction, SABESP began to indirectly hold such investments through SABESP Participações. This is an intra-group corporate reorganization, which did not result in an effect on the Company's shareholders' equity, cash or consolidated results.

EMAE

With the acquisition of EMAE’s control, as well as the additional acquisition of shares held by non-controlling shareholders in January 2026, the Company became the holder of 79.31% of said company. For further details, see Note 4.

The Company holds equity interest valued under the equity method in the following investees:

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

	Equity			Additions	Write-offs	Dividends	Comprehensive Income	Profit (loss) for the Period			Equity Interest Percentage
	March 31, 2026	December 31, 2025		January to March 2026	January to March 2026	January to March 2026	January to March 2026	January to March 2026	*()**	January to March 2025	March 31, 2026	December 31, 2025

Sesamm	95,110	91,455	—	—	—	—	—	3,655	—	4,722	36 %	36 %
Águas de Andradina	—	41,291	—	—	(41,291)	—	—	—	—	1,397	— %	30 %
Águas de Castilho	—	12,060	—	—	(12,060)	—	—	—	—	603	— %	30 %
Attend Ambiental	60,841	60,961	—	—	—	(6,450)	—	6,330	—	9,309	45 %	45 %
Aquapolo Ambiental	151,984	143,988	—	—	—	—	—	7,996	—	10,485	49 %	49 %
Paulista Geradora de Energia	23,544	22,769	—	—	—	—	—	775	—	174	25 %	25 %
Cantareira SP Energia	11,046	10,975	—	—	—	—	—	70	1	8	49 %	49 %
Barueri Energia Renovável	250,623	252,212	—	—	—	—	—	(1,589)	—	(1,620)	20 %	20 %
SABESP Luxembourg	7,162	8,452	—	—	—	—	(426)	(864)	—	—	100 %	100 %
SABESP Participações	103,012	85,001	—	15,649	(15,649)	—	—	2,362	—	—	100 %	100 %
SABESP Olímpia	165,648	162,671	—	—	—	—	—	2,977	—	1,219	100 %	100 %
EMAE (***)	594,823	—		594,823	—	—	—	—	—	—	79 %	—
Concessionária Sabesp URAE-1	1	1		—	—	—	—	—	—	—	100 %	100 %

(*) The amount presented refers to the changes in the investee’s equity, since its financial statements for the year ended December 31, 2025 were issued after the disclosure of SABESP’s financial statements.

(**) Refers to amounts as of January 1, 2026. See Note 4 for further details.

The balances of investments and the respective changes are as follows:

	Individual
	Investments		Additions	Write-off	Dividends	Comprehensive Income	Reclassification ()**	Equity Accounting
	March 31, 2026	December 31, 2025	January to March 2026	January to March 2026	January to March 2026	January to March 2026	January to March 2026	January to March 2026	*()**	January to March 2025
									—
Sesamm	34,240	32,924	—	—	—	—	—	1,316	—	1,700
Águas de Andradina	—	12,387	—	(12,201)	—	—	—	(186)	—	418
Águas de Castilho	—	3,618	—	(3,447)	—	—	—	(171)	—	181
Attend Ambiental	27,379	27,433	—	—	(2,903)	—	—	2,849	—	4,189
Aquapolo Ambiental	74,473	70,555	—	—	—	—	—	3,918	—	5,138
Paulista Geradora de Energia	5,886	5,693	—	—	—	—	—	193	—	45
Cantareira SP Energia	5,412	5,378	—	—	—	—	—	34	—	9
Barueri Energia Renovável	50,126	50,443	—	—	—	—	—	(317)	—	(324)
Infranext	—	—	—	—	—	—	—	—	—	—
SABESP Luxembourg	7,162	8,452	—	—	—	(426)	—	(864)	—	—
SABESP Participações	103,012	85,001	15,649	—	—	—	—	2,362	—	—
SABESP Olímpia	165,648	162,670	—	—	—	—	—	2,978	—	1,219
EMAE	471,754	—	471,754	—	—	—	—	—	—	—

Total	945,092	464,554	487,403	(15,648)	(2,903)	(426)	—	12,112		12,575

Others investments	534,217	29,534

Total	1,479,309	494,088

(*) The amount presented refers to changes in the equity of the investee, as its financial statements for the year ended December 31, 2025 were issued after the disclosure of SABESP’s financial statements.

(**) The amount of the investee's loss in excess of the investment was reclassified to Non-current Liabilities.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

	Consolidated
	Investments		Dividends	Equity Accounting
	March 31, 2026	December 31, 2025	January to March 2026	January to March 2026	*()**	January to March 2025

Sesamm	34,240	32,924	—	1,316	—	1,700
Águas de Andradina	12,569	12,387	—	182	—	418
Águas de Castilho	3,754	3,618	—	136	—	181
Attend Ambiental	27,379	27,433	(2,903)	2,849	—	4,189
Aquapolo Ambiental	74,473	70,555	—	3,918	—	5,138
Paulista Geradora de Energia	5,886	5,693	—	193	—	45
Cantareira SP Energia	5,412	5,378	—	34	—	9
Barueri Energia Renovável	50,126	50,443	—	(317)	—	(324)

Total	213,839	208,431	(2,903)	8,311	—	11,356

Other investments	29,307	45,927

Total	243,146	254,358

13 Contract assets and other concession assets

	Individual
	December 31, 2025	Additions (i)	Write-offs	Transfers	Transfers to intangible assets (ii)	Transfer to the concession’s financial assets	March 31, 2026 (iii)

Contract Assets and other concession assets	11,006,489	3,755,847	—	—	(388,658)	(118,062)	14,255,616

	Consolidated
	December 31, 2025	Additions (i)	Write-offs	Transfers	Transfers to intangible assets (ii)	Transfer to the concession’s financial assets	March 31, 2026 (iii)

Contract Assets and other concession assets	11,018,516	3,756,449	—	—	(388,658)	(118,062)	14,268,245

	Individual
	December 31, 2024	Additions	Write-offs	Transfers	Transfers to intangible assets	Transfer to the concession’s financial assets	March 31, 2025

Contract Assets and other concession assets	4,872,410	2,788,002	—	3	(589,908)	(168,104)	6,902,403

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

	Consolidated
	December 31, 2024	Additions	Write-offs	Transfers	Transfers to intangible assets	Transfer to the concession’s financial assets	December 31, 2025

Contract Assets and other concession assets	4,877,667	2,789,029	—	3	(589,908)	(168,104)	6,908,687

(i)

The largest additions in the period were located in the municipalities of São Paulo, Guarulhos, and Praia Grande, in the amounts of R$ 1,490 million, R$ 346 million and R$ 141 million, respectively. Furthermore, the Company recognizes in the additions other concession assets:

Other concession assets (changes)	Individual	Consolidated
Other additions (iv)	123,138	123,138
Construction Revenue (Note 31)	3,632,709	3,633,311
Total additions	3,755,847	3,756,449

(ii)

The largest transfers in the period were located in the municipalities of São Paulo, Guarulhos, and Franca, totaling R$ 190 million, R$ 29 million, and R$ 22 million, respectively.

(iii)

The largest works are located in the municipalities of São Paulo, Guarulhos and Praia Grande, totaling R$ 4,514 million, R$ 1,081 million, and R$ 446 million, respectively.

(iv)

Refers to other additions that did not have construction revenue as a corresponding offset, consisting mainly of advances and inventories related to construction projects, software, and provisions for unrecorded invoices.

As of March 31, 2026, and December 31, 2025, the contract asset and other concession assets had no amounts recognized as right-of-use leases.

(a)

Capitalization of interest and other finance charges

The Company capitalizes interest, inflation adjustments, and exchange rate changes in contract assets and other concession assets during the construction period. From January to March 2026, the Company capitalized R$ 233,801 (R$ 173,738 from January to March 2025).

(b) Expropriations

As a result of the construction of priority projects related to water and sewage systems, the Company is required to expropriate third-party properties, whose owners are compensated either amicably or in court. The costs of such expropriations are recorded in the contract asset and other concession assets during the execution of the works. From January to March 2026, the total amount referring to expropriations was R$ 10,938 (from January to March 2025 – R$ 14,446).

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

14 Intangible assets

(a) Statement of financial position details

	Individual
	March 31, 2026			December 31, 2025
	Cost	Amortization	Net	Cost	Amortization	Net

Intangible assets arising from:
Concession agreements - others	135,321	(61,060)	74,261	135,470	(60,381)	75,089
Contract Commitments (i)	4,437,857	(740,756)	3,697,101	4,437,857	(707,736)	3,730,121
Concession Agreements - URAE-1	69,665,817	(23,905,142)	45,760,675	69,281,545	(23,335,074)	45,946,471
Software license of use	1,696,773	(1,191,411)	505,362	1,696,773	(1,145,671)	551,102
Right of use – other assets	240,646	(206,200)	34,446	240,646	(188,678)	51,968
Total	76,176,414	(26,104,569)	50,071,845	75,792,291	(25,437,540)	50,354,751

	Consolidated
	March 31, 2026				December 31, 2025
	Cost	Amortization	Goodwill	Net	Cost	Accumulated Amortization	Net

Intangible assets arising from:
Concession agreements - new contracts	148,000	(11,511)	-	136,489	148,000	(10,275)	137,725
Concession agreements - others	135,321	(61,060)	-	74,261	135,470	(60,381)	75,089
Contract Commitments (i)	4,437,857	(740,756)	-	3,697,101	4,437,857	(707,736)	3,730,121
Concession Agreements - URAE-1	69,665,817	(23,905,142)	-	45,760,675	69,281,545	(23,335,074)	45,946,471
Software license of use	1,728,294	(1,203,681)	-	524,613	1,696,773	(1,145,671)	551,102
Right of use – other assets	240,646	(206,200)	-	34,446	240,646	(188,681)	51,965
Goodwill/identifiable asset	504,910	-	-	504,910	—	—	—
Total	76,860,845	(26,128,350)	-	50,732,495	75,940,291	(25,447,818)	50,492,473

(i) With the enactment of the Basic Sanitation Law in 2007, contract renewals began to be executed through program agreements, under which the Company assumed assets and socio environmental obligations and recognized them as intangible assets, which are amortized on a straight-line basis over the term of the agreements.

(b) Changes

	Individual
	December 31, 2025	Additions	Transfer of contract asset and other concession assets	Transfers	Write-offs and disposals	Amortization	March 31, 2026

Intangible assets arising from:
Concession agreements – others	75,089	—	222	(2)	—	(1,048)	74,261
Contract Commitments	3,730,121	—	—	—	—	(33,020)	3,697,101
Concession Agreements URAE-1 (*)	45,946,471	—	388,436	8,010	(393)	(581,849)	45,760,675
Software license of use	551,102	—	—	—	—	(45,740)	505,362
Right of use – other assets	51,968	—	—	—	—	(17,522)	34,446
Total	50,354,751	—	388,658	8,008	(393)	(679,179)	50,071,845

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

	Consolidated
	December 31, 2025	Additions	Transfer of contract asset	Transfers	Write-offs and disposals	Amortization	Business combination (Note 4)	March 31, 2026

Intangible assets arising from:
Concession agreements – new contracts	137,723	—	—	—	—	(1,235)	—	136,488
Concession agreements – others	75,088	—	222	(2)	—	(1,048)	—	74,260
Contract Commitments	3,730,121	—	—	—	—	(33,020)	—	3,697,101
Concession Agreements URAE-1 (*)	45,946,471	—	388,436	8,010	(393)	(581,849)	—	45,760,675
Software license of use	551,102	—	—	—	—	(45,740)	19,253	524,615
Right of use – other assets	51,968	—	—	—	—	(17,522)	—	34,446
Goodwill/identifiable asset	—	—	—	—	—	—	504,910	504,910
Total	50,492,473	—	388,658	8,008	(393)	(680,414)	524,163	50,732,495

(*) As of March 31, 2026, the line URAE-1 concession agreement included leases totaling R$ 149,164 (R$ 154,449 as of December 31, 2025). Also on this date, the accounting balance of intangible assets, contract assets and other concession assets, and financial assets of the concession aimed at URAE-1 amounted to R$ 83,208,920, accounting for 95.57% of the consolidated amount.

	Individual
	December 31, 2024	Additions	Transfer of contract asset	Transfers	Write-offs and disposals	Amortization	Transfer to Financial Assets	March 31, 2025

Intangible assets arising from:
Concession agreements – others	59,492	—	10	12	—	(1,075)	—	58,439
Contract Commitments	3,849,759	—	—	—	—	(32,117)	—	3,817,642
Concession Agreements URAE-1 (*)	39,956,194	1,245	747,688	21,429	(874)	(472,288)	(168,104)	40,085,290
Software license of use	638,287	—	10,314	—	—	(48,338)	—	600,263
Right of use – other assets	124,736	—	—	—	—	(19,127)	—	105,609
Total	44,628,468	1,245	758,012	21,441	(874)	(572,945)	(168,104)	44,667,243

	Consolidated
	December 31, 2024	Additions		Transfer of contract asset		Transfers	Write-offs and disposals	Amortization	Transfer to Financial Assets	March 31, 2025

Intangible assets arising from:
Concession agreements – new contracts	142,656	—	—	—	—	—	—	(1,234)	—	141,422
Concession agreements – others	59,492			10		12	—	(1,075)	—	58,439
Contract Commitments	3,849,759	—	—	—	—	—	—	(32,117)	—	3,817,642
Concession Agreements URAE-1 (*)	39,956,194	1,245		747,688		21,429	(874)	(472,288)	(168,104)	40,085,290
Software license of use	638,287	—		10,314		—	—	(48,338)	—	600,263
Right of use – other assets	124,736	—		—		—	—	(19,127)	—	105,609
Total	44,771,124	1,245		758,012		21,441	(874)	(574,179)	(168,104)	44,808,665

(*) As of March 31, 2025, the line URAE-1 concession agreement included leases totaling R$ 329,624 (R$ 338,740 as of December 31, 2024), respectively.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

(c) Public-Private Partnership - PPP

SABESP carries out transactions related to the Public-Private Partnership. Such transactions, along with their corresponding guarantees and obligations, are supported by a contract established based on Law No. 11,079/2004.

The amounts recorded in intangible assets, item Concession Agreements URAE-1, are shown in the table below:

	Individual and Consolidated
Nature	March 31, 2026	December 31, 2025

Alto Tietê	198,775	202,823
São Lourenço	2,174,008	2,216,444

As of March 31, 2026, and December 31, 2025, the obligations assumed by the Company are as follows:

	Individual and Consolidated
	March 31, 2026			December 31, 2025
	Current liabilities	Non-current liabilities	Total liabilities	Current liabilities	Non-current liabilities	Total liabilities
São Lourenço	473,049	2,851,931	3,324,980	469,687	2,856,008	3,325,695

The chart below shows expenses with Public-Private Partnership from January to March 2026, compared to the figures reported in the same period in 2024:

	Individual and Consolidated
Nature	January to March 2026	January to March 2025

General supplies	5,484	5,188
Outsourced services	11,572	10,948
General expenses	1,515	1,434
Amortization	42,437	42,437
Financial expenses	122,675	142,252
Total	183,683	202,259

(d) Amortization of intangible assets

The average amortization rate was 3.57% and 2.6% as of March 31, 2026 and 2025, respectively.

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

(e) Leases and right of use

	Individual and Consolidated
Nature	March 31, 2026	December 31, 2025

Leases - Concession Agreement URAE-1
Cost	404,978	405,245
Accumulated amortization	(255,814)	(250,796)
(=) Net	149,164	154,449

Right of use - Other assets
Vehicles	216,428	216,428
Properties	24,142	24,142
Equipment	76	76
Accumulated amortization	(206,200)	(188,678)
(=) Net	34,446	51,968

Total - Leases and Right of use	183,610	206,417

The lease liability corresponds to total future fixed lease payments, adjusted to present value, considering an incremental rate on borrowings. For further information, see Note 17.

The table below shows the impact on the Company’s profit or loss:

	Individual and Consolidated
	March 31, 2026	March 31, 2025

Right of use amortization	(22,808)	(28,244)
Financial result – interest expense and inflation adjustment	(30,922)	(38,493)
Expenses of short-term and low-value leases	(8,543)	(10,533)
Decrease in profit for the period	(62,273)	(77,270)

(f) Performance Agreements

The accounting balances of current agreements recorded in the contract assets and other concession assets and intangible assets are as follows:

	Individual and Consolidated
	March 31, 2026	December 31, 2025
Contract assets and other concession assets	405,835	601,064
Intangible assets	1,089,043	1,077,363
Total	1,494,878	1,678,427

As of March 31, 2026, and December 31, 2025, the obligations assumed by the Company are as follows:

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

	Individual and Consolidated
	March 31, 2026			December 31, 2025
	Current liabilities	Non-current liabilities	Total liabilities	Current liabilities	Non-current liabilities	Total liabilities

Performance Agreements	125,766	3,543	129,309	120,776	6,151	126,927

15 Financial asset of the concession

With the completion of the privatization process and signing of the agreement with URAE-1 in July 2024, resulting in a single agreement covering 371 municipalities with a new expiration date in 2060, which provided greater legal security and granted an unconditional right to receive cash at the end of the concession, the Company recognized a modification in the agreement, leading to a bifurcation of concession assets considering the contractual right that reversible investments and not fully amortized by the end of the agreement must be compensated.

The impacts of Income and Social Contribution Taxes and PIS and Cofins are deferred until the time of their realization.

The change in the balance of the concession’s financial asset is as follows:

	Individual
	December 31, 2025	Transfer of contract asset (a)	Financial Asset of the Concession - Restatement (b)	March 31, 2026

Financial Asset of the Concession
Concession Agreement - URAE-1	21,665,330	118,062	342,487	22,125,879

	Consolidated
	December 31, 2025	Transfer of contract asset (a)	Financial Asset of the Concession - Restatement (b)	Business combination (Note 4)	March 31, 2026

Financial Asset of the Concession
Concession Agreement - URAE-1	21,665,330	118,062	342,487	—	22,125,879
Other - EMAE	—	—	—	195,375	195,375
Total	21,665,330	118,062	342,487	195,375	22,321,254

	Individual and Consolidated
	December 31, 2024	Transfer of contract asset (a)	Financial Asset of the Concession - Restatement (b)	March 31, 2025

Financial Asset of the Concession
Concession Agreement - URAE-1	17,601,626	168,104	420,229	18,189,959

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

(a) Correspond to transfers (bifurcation) of contract assets and other concession assets to the concession’s financial asset, which were previously recognized at their cost;

(b) Review of the financial asset considering the restatement using the IPCA, as this is the rate used by the regulatory agency for the adjustment of assets to be compensated.

16 Property, plant, and equipment

(a)

Statement of financial position details

	Individual
	March 31, 2026				December 31, 2025
	Cost	Depreciation	Net	Useful life	Cost	Depreciation	Net	Useful life

Land	101,258	(363)	100,895	—	94,001	—	94,001	—
Buildings	133,757	(49,843)	83,914	50 years	134,818	(49,179)	85,639	50 years
Equipment	636,363	(356,127)	280,236	5 - 20 years	629,653	(346,037)	283,616	5 - 20 years
Transportation equipment	140,475	(21,637)	118,838	10 years	126,689	(18,394)	108,295	10 years
Furniture and fixtures	41,673	(19,731)	21,942	15 years	41,465	(19,141)	22,324	15 years
Energy generation infrastructure	165,100	(20,810)	144,290	15 - 20 years	165,100	(18,084)	147,016	15 - 20 years
Other	7,279	(666)	6,613	20 years	7,278	(620)	6,658	20 years
Property, plant and equipment in progress	158,927	—	158,927	—	143,242	—	143,242	—
Total	1,384,832	(469,177)	915,655	—	1,342,246	(451,455)	890,791	—

	Consolidated
	March 31, 2026				December 31, 2025
	Cost	Depreciation	Net	Useful life	Cost	Depreciation	Net	Useful life

Land	105,541	(363)	105,178	— %	94,001	—	94,001	—%
Buildings	177,667	(51,024)	126,643	50 years	134,818	(49,179)	85,639	50 years
Equipment	690,270	(358,991)	331,279	5 - 20 years	629,653	(346,037)	283,616	5 - 20 years
Transportation equipment	140,555	(21,645)	118,910	10 years	126,689	(18,394)	108,295	10 years
Furniture and fixtures	41,968	(19,761)	22,207	15 years	41,465	(19,141)	22,324	15 years
Energy generation infrastructure	165,100	(20,810)	144,290	15 - 20 years	165,100	(18,084)	147,016	15 - 20 years
Reservoirs, dams and pipelines	40,845	(1,071)	39,774	50 years	-	-	-	—%
Other	16,709	(823)	15,886	20 years	7,278	(620)	6,658	20 years
Property, plant and equipment in progress	231,045	(10,449)	220,596	— %	143,242	—	143,242	—%
Total	1,609,700	(484,937)	1,124,763	—	1,342,246	(451,455)	890,791	—

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

(b)

Changes

	Individual
	December 31, 2025	Additions	Transfers	Write-offs and disposals	Depreciation	March 31, 2026

Land	94,001	-	6,894	-	-	100,895
Buildings	85,639	-	(18)	(1,149)	(558)	83,914
Equipment	283,616	-	6,521	(36)	(9,865)	280,236
Transportation equipment	108,295	-	13,835	(9)	(3,283)	118,838
Furniture and fixtures	22,324	-	199	-	(581)	21,942
Energy generation infrastructure	147,016	-	-	-	(2,726)	144,290
Other	6,658	-	-	-	(45)	6,613
Property, plant and equipment in progress	143,242	33,955	(18,270)	-	-	158,927
Total	890,791	33,955	9,161	(1,194)	(17,058)	915,655

	Consolidated
	December 31, 2025	Additions	Transfers	Write-offs and disposals	Depreciation	Business combination (Note 4)	March 31, 2026

Land	94,001	—	6,894	—	—	4,283	105,178
Buildings	85,639	—	(18)	(1,149)	(558)	42,279	126,643
Equipment	283,616	—	6,521	(36)	(9,865)	51,043	331,279
Transportation equipment	108,295	—	13,835	(9)	(3,283)	72	118,910
Furniture and fixtures	22,324	—	199	—	(581)	265	22,207
Energy generation infrastructure	147,016	—	—	—	(2,726)	-	144,290
Reservoirs, dams and pipelines	—	—	—	—	—	39,774	39,774
Other	6,658	—	—	—	(45)	9,273	15,886
Property, plant and equipment in progress	143,242	33,955	(18,270)	—	—	61,669	220,596
Total	890,791	33,955	9,161	(1,194)	(17,058)	209,108	1,124,763

	Individual and Consolidated
	December 31, 2024	Additions	Transfers	Write-offs and disposals	Depreciation	March 31, 2025

Land	94,751	62	(33)	—	—	94,780
Buildings	80,920	-	209	—	(527)	80,602
Equipment	149,744	-	9,636	(54)	(5,332)	153,994
Transportation equipment	23,538	-	19,807	—	(826)	42,519
Furniture and fixtures	20,779	-	1,724	(6)	(549)	21,948
Energy generation infrastructure	121,533	-	5	—	(2,096)	119,442
Other	6,930	-	-	—	(48)	6,882
Property, plant and equipment in progress	63,353	60,674	(26,320)	—	—	97,707
Total	561,548	60,736	5,028	(60)	(9,378)	617,874

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

17	Borrowings and financing

Borrowings and financing outstanding balance	Individual
	March 31, 2026			December 31, 2025
Financial institution	Current	Non-current	Total	Current	Non-current	Total

Local currency
Debentures	2,768,889	25,637,595	28,406,484	2,764,582	20,230,117	22,994,699
Brazilian Federal Savings Bank	137,030	1,467,440	1,604,470	134,275	1,495,481	1,629,756
BNDES	259,709	504,300	764,009	259,341	564,501	823,842
IDB	298,509	2,554,865	2,853,374	307,349	2,680,484	2,987,833
IFC	22,650	2,006,802	2,029,452	64,450	2,645,882	2,710,332
Leases (Concession)	74,650	110,178	184,828	84,214	110,214	194,428
Leases (Other)	70,172	7,724	77,896	72,440	9,627	82,067
Other	483	725	1,208	616	328	944
Interest	848,930	—	848,930	1,139,091	—	1,139,091

Total in local currency	4,481,022	32,289,629	36,770,651	4,826,358	27,736,634	32,562,992

Foreign currency
IDB	53,661	904,542	958,203	56,573	973,833	1,030,406
IBRD	31,731	1,011,545	1,043,276	33,453	1,112,127	1,145,580
JICA	140,783	1,732,536	1,873,319	150,779	1,965,688	2,116,467
IFC	—	3,158,572	3,158,572	—	3,380,431	3,380,431
A/B Blue Bonds	—	8,017,482	8,017,482	—	—	—
Interest	176,930	—	176,930	65,727	—	65,727
Total in foreign currency	403,105	14,824,677	15,227,782	306,532	7,432,079	7,738,611

Total borrowings and financing	4,884,127	47,114,306	51,998,433	5,132,890	35,168,713	40,301,603

Companhia de Saneamento Básico do Estado de São Paulo – SABESP

Notes to the Financial Statements for the

Period ended March 31, 2026

In thousands of reais, unless otherwise stated

Borrowings and financing outstanding balance	Consolidated
	March 31, 2026				December 31, 2025
Financial institution	Current	Non-current		Total	Current	Non-current	Total

Local currency
Debentures	2,768,889	22,655,074		25,423,963	2,764,582	17,282,427	20,047,009
Brazilian Federal Savings Bank	137,030	1, 467,440		1,604,470	134,275	1,495,481	1,629,756
BNDES	259,709	504,300		764,009	259,341	564,501	823,842
IDB	298,509	2,554,865	<

COMPANHIA DE SANEAMENTO BASICO DO ESTADO DE SAO PAULO-SABESP 6-K