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Stanislaus County, California — public water systems

At a glance

191 active public water systems are filed under Stanislaus County, California in EPA's SDWIS records, together reporting 512,656 people served. The largest is City of Modesto, which reports serving 218,771 people. 60 are community water systems serving people where they live; the other 131 are non-community systems, such as schools, workplaces, campgrounds and gas stations with their own supply.

Dataset updated . Source: EPA SDWIS/ECHO, refreshed quarterly.

Active systems

191

Population served

512.7K

Community systems

60

Groundwater share

92.7%

How does Stanislaus County compare with other California counties?

Stanislaus County has the 12th-most active public water systems among the 201 counties listed for active California systems in EPA records; among the 72 with 3 or more systems, the median has 73. Its systems report 512,656 people served in total, the 16th-largest county figure in the state and 1.2% of the statewide total. The average system here reports serving 2,684 people, about half of the California average of 5,706. Population figures are what each system reports; people served by more than one system, such as a wholesaler and the town that buys from it, are counted by each.

Where does Stanislaus County's drinking water come from?

By primary water source, Stanislaus County's active systems draw on groundwater (174, 91%), purchased surface water (8, 4.2%), surface water (6, 3.1%) and purchased groundwater (2, 1%). Overall, 93% rely mainly on groundwater (including purchased groundwater) and 7.3% on surface water, compared with 85% and 15% across California. Groundwater means the system draws its water from wells or springs fed by underground aquifers. The county's largest system, City of Modesto, draws primarily on purchased surface water.

What kinds of water systems operate in Stanislaus County?

Stanislaus County's active systems break down as 60 community systems (31%), 64 non-transient non-community systems (34%) and 67 transient non-community systems (35%). A community water system serves at least 15 connections used by year-round residents, or regularly serves at least 25 year-round residents. Homes, apartments and mobile-home parks are served by these. A non-transient non-community water system regularly serves at least 25 of the same people for more than six months a year, but not where they live. Schools, factories, office buildings and hospitals with their own supply are typical examples. A transient non-community water system serves places where people do not stay long, such as gas stations and campgrounds, and regularly serves at least 25 people a day for at least 60 days a year. EPA lists their owner types as private (68%), local government (30%), federal government (1%) and state government (0.5%).

The 50 largest water systems in Stanislaus County

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Active public water systems in Stanislaus County, California
#Water systemCountyPopulation servedTypeSource
1Modesto, City ofStanislaus218,771CommunityPurchased surface water
2Turlock, City ofStanislaus72,682CommunityPurchased surface water
3Ceres, City ofStanislaus54,513CommunityPurchased surface water
4Patterson, City ofStanislaus24,977CommunityGroundwater
5Riverbank, City ofStanislaus24,834CommunityGroundwater
6Oakdale, City ofStanislaus23,235CommunityGroundwater
7City of Modesto - SalidaStanislaus14,537CommunityPurchased surface water
8City of Newman-Water DepartmentStanislaus12,207CommunityGroundwater
9City of WaterfordStanislaus8,788CommunityGroundwater
10Hughson, City ofStanislaus7,481CommunityGroundwater
11Keyes Community Services Dist.Stanislaus5,672CommunityGroundwater
12Denair Community Services DistrictStanislaus5,090CommunityGroundwater
13Joe'S Travel Plaza (Eh)Stanislaus5,026Non-transient non-communityGroundwater
14Department of TransportationStanislaus4,375Transient non-communityGroundwater
15Western Hills Water District/Diablo GranStanislaus2,000CommunitySurface water
16Gregori High SchoolStanislaus2,000Non-transient non-communityGroundwater
17Oid-Oakdale Rural Water System #1Stanislaus1,570CommunityGroundwater
18City of Modesto - Del RioStanislaus1,327CommunityGroundwater
19City of Modesto - South TurlockStanislaus1,099CommunityPurchased surface water
20Waterford-River PointeStanislaus1,079CommunityGroundwater
21Our Lady of Assumption ChurchStanislaus1,000Transient non-communityGroundwater
22City of Modesto - GraysonStanislaus914CommunityGroundwater
23Hillsview HomesStanislaus887CommunityGroundwater
24Mesa Elementary SchoolStanislaus860Non-transient non-communityGroundwater
25Hart- Ransom Union School & DistrictStanislaus650Non-transient non-communityGroundwater
26Riverdale Park Tract CsdStanislaus610CommunityGroundwater
27Waterford - HickmanStanislaus597CommunityGroundwater
28Riverview Mobile Home EstatesStanislaus540CommunityGroundwater
29Woodward Reservoir Water SystemStanislaus537Transient non-communityGroundwater
30Jehovah'S Witness Sierra Vista CongStanislaus500Transient non-communityGroundwater
31River Oak Grace-Water SystemStanislaus500Transient non-communityGroundwater
32River Oaks/Kingdom HallStanislaus500Transient non-communityGroundwater
33Crows Landing Comm Svc DistrictStanislaus500CommunityGroundwater
34Ceres Unified/Westport SchoolStanislaus450Non-transient non-communityGroundwater
35Bronco WineryStanislaus400Non-transient non-communityGroundwater
36Stanislaus Union School DistStanislaus390Non-transient non-communityGroundwater
37Chatom School (Eh)Stanislaus385Non-transient non-communityGroundwater
385033 PentecostStanislaus302Non-transient non-communityGroundwater
39Nmip Fire & Water System, LLCStanislaus300Non-transient non-communityGroundwater
40Covenant Grove ChurchStanislaus300Transient non-communityGroundwater
41Oid #51 - Sunset Oaks #10Stanislaus287CommunityGroundwater
42Oid #46 - Sunset OaksStanislaus269CommunityGroundwater
43Park Heights Mutual Water CoStanislaus250CommunityGroundwater
44Ram Naam Mandali Church of ModestoStanislaus250Transient non-communityGroundwater
45North Oaks Mutual Water CoStanislaus234CommunityGroundwater
46Paradise SchoolStanislaus218Non-transient non-communityGroundwater
47Casa De Amigos Manufactured Housing CommStanislaus204CommunityGroundwater
48The Morning Star CompanyStanislaus200Non-transient non-communityGroundwater
49Tid/ La Grange Water SystemStanislaus195CommunitySurface water
50Monte Vista FarmingStanislaus188Non-transient non-communityGroundwater

All other water systems in Stanislaus County (140)

The remaining active systems filed under Stanislaus County, largest first, with the population each reports serving.

Stanislaus County water systems: frequently asked questions

How many public water systems are in Stanislaus County, California?

EPA's SDWIS records file 191 active public water systems under Stanislaus County, California: 60 community systems (31%), 64 non-transient non-community systems (34%) and 67 transient non-community systems (35%).

Who supplies drinking water in Stanislaus County, CA?

The largest community water systems filed under Stanislaus County are City of Modesto (218,771 people served), City of Turlock (72,682 people served) and City of Ceres (54,513 people served). Which system serves a particular address depends on its service area, which EPA's SDWIS records do not include; a water bill or the local utility can confirm it.

Does Stanislaus County's drinking water come from groundwater or surface water?

Of the 191 active public water systems in Stanislaus County, 93% draw mainly on groundwater and 7.3% on surface water, counting purchased supplies. The largest system, City of Modesto, uses purchased surface water.

Where can I find a water quality report for Stanislaus County?

Each community water system must deliver an annual water quality report, called a Consumer Confidence Report, to its customers by July 1, covering the previous calendar year. 60 community systems are filed under Stanislaus County, so the report to look for is the one from the system that supplies your address.

How can I check violations for a water system in Stanislaus County?

Open the system's profile from the list on this page. Each profile shows the most recent Safe Drinking Water Act violations in EPA's records, with plain-English labels and whether each one is resolved. For current compliance status, EPA ECHO is the primary source.

More California water systems

About this data

Source: U.S. EPA Safe Drinking Water Information System (SDWIS) and SDWA violation records, via EPA ECHO, as published October 1, 2026 — AquaCensus refreshes it quarterly. See the methodology for how records are matched, cleaned and scored.

Cite as: AquaCensus, “Public water systems in Stanislaus County, California”, https://aquacensus.com/water-systems/california/stanislaus (data as of October 1, 2026).