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San Luis Obispo County, California — public water systems

At a glance

171 active public water systems are filed under San Luis Obispo County, California in EPA's SDWIS records, together reporting 348,510 people served. The largest is Santa Margarita Recreation Area, which reports serving 50,001 people. 73 are community water systems serving people where they live; the other 98 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

171

Population served

348.5K

Community systems

73

Groundwater share

81.3%

How does San Luis Obispo County compare with other California counties?

San Luis Obispo County has the 15th-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 348,510 people served in total, the 23rd-largest county figure in the state and 0.8% of the statewide total. The average system here reports serving 2,038 people, about 64% below 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 San Luis Obispo County's drinking water come from?

By primary water source, San Luis Obispo County's active systems draw on groundwater (137, 80%), purchased surface water (19, 11%), surface water (13, 7.6%) and groundwater under influence of surface water (2, 1.2%). Overall, 81% rely mainly on groundwater (including purchased groundwater) and 19% 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, Santa Margarita Recreation Area, draws primarily on groundwater.

What kinds of water systems operate in San Luis Obispo County?

San Luis Obispo County's active systems break down as 73 community systems (43%), 54 non-transient non-community systems (32%) and 44 transient non-community systems (26%). 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 (76%), local government (19%), state government (3.5%) and federal government (1.2%).

The 50 largest water systems in San Luis Obispo County

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Active public water systems in San Luis Obispo County, California
#Water systemCountyPopulation servedTypeSource
1Santa Margarita Recreation AreaSan Luis Obispo50,001Transient non-communityGroundwater
2San Luis Obispo Water DepartmentSan Luis Obispo47,788CommunitySurface water
3City of Paso Robles Water DivisionSan Luis Obispo31,176CommunitySurface water
4Atascadero Mutual Water CoSan Luis Obispo30,618CommunityGroundwater
5City of Arroyo Grande Utilities DivisionSan Luis Obispo17,963CommunityPurchased surface water
6California Mens ColonySan Luis Obispo15,000CommunitySurface water
7Nipomo Comm Services DistSan Luis Obispo13,771CommunityPurchased surface water
8Morro Bay Pw Dept - Water DivisionSan Luis Obispo13,757CommunityPurchased surface water
9City of Grover Beach Public Works DeptSan Luis Obispo12,701CommunitySurface water
10Brecon EstateSan Luis Obispo9,012Transient non-communityGroundwater
11Pismo Beach Water DepartmentSan Luis Obispo8,036CommunityPurchased surface water
12Templeton CsdSan Luis Obispo8,011CommunityGroundwater
13Oceano Comm Services Dist.San Luis Obispo7,601CommunityPurchased surface water
14Los Osos Community Services DistrictSan Luis Obispo7,086CommunityGroundwater
15Golden State Water Company - Los OsosSan Luis Obispo5,924CommunityGroundwater
16Cambria Comm Services DistSan Luis Obispo5,532CommunityGroundwater
17Golden State Water Company - NipomoSan Luis Obispo4,506CommunityPurchased surface water
18Atascadero State HospitalSan Luis Obispo4,100CommunityGroundwater
19Woodlands DevelopmentSan Luis Obispo3,862CommunityPurchased surface water
20Grosso Kresser WinerySan Luis Obispo3,606Transient non-communityGroundwater
21Heritage Ranch CsdSan Luis Obispo2,956CommunitySurface water
22San Miguel Community Services DistrictSan Luis Obispo2,600CommunityGroundwater
23Cayucos Beach Mutual Water CompanySan Luis Obispo2,567CommunityPurchased surface water
24Morro Rock Mutual Water CoSan Luis Obispo2,181CommunityPurchased surface water
25Nacimiento Water CompanySan Luis Obispo2,181CommunitySurface water
26Golden State Water Company-Cypress RidgeSan Luis Obispo2,026CommunityGroundwater
27Avila Beach Community Services DistrictSan Luis Obispo1,630CommunityPurchased surface water
28San Miguelito MwcSan Luis Obispo1,600CommunityPurchased surface water
29Tiger Water SupplySan Luis Obispo1,600Non-transient non-communityGroundwater
30Lopez ProjectSan Luis Obispo1,569CommunitySurface water
31County of Monterey-Lake NacimientoSan Luis Obispo1,521Non-transient non-communityGroundwater under influence of surface water
32Golden State Water Company - EdnaSan Luis Obispo1,493CommunityGroundwater
33Caltrans - Shandon Rest StopSan Luis Obispo1,300Transient non-communityGroundwater
34Slo Cwwd No. 23 - Santa MargaritaSan Luis Obispo1,291CommunityGroundwater
35Slocsa #10a - CayucosSan Luis Obispo1,200CommunityPurchased surface water
36Pg&ESan Luis Obispo1,200Non-transient non-communitySurface water
37Slo Csa No. 16 - ShandonSan Luis Obispo1,085CommunityPurchased surface water
38Daou Vineyards, LLCSan Luis Obispo1,025Non-transient non-communityGroundwater
39Montana De Oro State ParkSan Luis Obispo990Transient non-communitySurface water
40Laureate Water CompanySan Luis Obispo700CommunityGroundwater
41Coastal Christian SchoolSan Luis Obispo650Non-transient non-communityGroundwater
42Mesa Dunes Mobile Home EstatesSan Luis Obispo600CommunityGroundwater
43S & T Mutual Water CompanySan Luis Obispo591CommunityGroundwater
44Woodland Park Mutual Water CoSan Luis Obispo538CommunityGroundwater
45The AndersonSan Luis Obispo500Transient non-communityGroundwater
46Hearst Memorial State BeachSan Luis Obispo500Transient non-communityPurchased surface water
47Walnut Hills Mutual Water CoSan Luis Obispo486CommunityGroundwater
48San Simeon CsdSan Luis Obispo462CommunityGroundwater
49Garden Farms C.W.D.San Luis Obispo440CommunityGroundwater
50Los Robles Mobile Home EstatesSan Luis Obispo420CommunityGroundwater

All other water systems in San Luis Obispo County (118)

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

San Luis Obispo County water systems: frequently asked questions

How many public water systems are in San Luis Obispo County, California?

EPA's SDWIS records file 171 active public water systems under San Luis Obispo County, California: 73 community systems (43%), 54 non-transient non-community systems (32%) and 44 transient non-community systems (26%).

Who supplies drinking water in San Luis Obispo County, CA?

The largest community water systems filed under San Luis Obispo County are San Luis Obispo Water Department (47,788 people served), City of Paso Robles Water Division (31,176 people served) and Atascadero Mutual Water Co (30,618 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 San Luis Obispo County's drinking water come from groundwater or surface water?

Of the 171 active public water systems in San Luis Obispo County, 81% draw mainly on groundwater and 19% on surface water, counting purchased supplies. The largest system, Santa Margarita Recreation Area, uses groundwater.

Where can I find a water quality report for San Luis Obispo 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. 73 community systems are filed under San Luis Obispo 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 San Luis Obispo 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 San Luis Obispo County, California”, https://aquacensus.com/water-systems/california/san-luis-obispo (data as of October 1, 2026).