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
🔒 Create a free account to export CSV| # | Water system | County | Population served | Type | Source |
|---|---|---|---|---|---|
| 1 | Santa Margarita Recreation Area | San Luis Obispo | 50,001 | Transient non-community | Groundwater |
| 2 | San Luis Obispo Water Department | San Luis Obispo | 47,788 | Community | Surface water |
| 3 | City of Paso Robles Water Division | San Luis Obispo | 31,176 | Community | Surface water |
| 4 | Atascadero Mutual Water Co | San Luis Obispo | 30,618 | Community | Groundwater |
| 5 | City of Arroyo Grande Utilities Division | San Luis Obispo | 17,963 | Community | Purchased surface water |
| 6 | California Mens Colony | San Luis Obispo | 15,000 | Community | Surface water |
| 7 | Nipomo Comm Services Dist | San Luis Obispo | 13,771 | Community | Purchased surface water |
| 8 | Morro Bay Pw Dept - Water Division | San Luis Obispo | 13,757 | Community | Purchased surface water |
| 9 | City of Grover Beach Public Works Dept | San Luis Obispo | 12,701 | Community | Surface water |
| 10 | Brecon Estate | San Luis Obispo | 9,012 | Transient non-community | Groundwater |
| 11 | Pismo Beach Water Department | San Luis Obispo | 8,036 | Community | Purchased surface water |
| 12 | Templeton Csd | San Luis Obispo | 8,011 | Community | Groundwater |
| 13 | Oceano Comm Services Dist. | San Luis Obispo | 7,601 | Community | Purchased surface water |
| 14 | Los Osos Community Services District | San Luis Obispo | 7,086 | Community | Groundwater |
| 15 | Golden State Water Company - Los Osos | San Luis Obispo | 5,924 | Community | Groundwater |
| 16 | Cambria Comm Services Dist | San Luis Obispo | 5,532 | Community | Groundwater |
| 17 | Golden State Water Company - Nipomo | San Luis Obispo | 4,506 | Community | Purchased surface water |
| 18 | Atascadero State Hospital | San Luis Obispo | 4,100 | Community | Groundwater |
| 19 | Woodlands Development | San Luis Obispo | 3,862 | Community | Purchased surface water |
| 20 | Grosso Kresser Winery | San Luis Obispo | 3,606 | Transient non-community | Groundwater |
| 21 | Heritage Ranch Csd | San Luis Obispo | 2,956 | Community | Surface water |
| 22 | San Miguel Community Services District | San Luis Obispo | 2,600 | Community | Groundwater |
| 23 | Cayucos Beach Mutual Water Company | San Luis Obispo | 2,567 | Community | Purchased surface water |
| 24 | Morro Rock Mutual Water Co | San Luis Obispo | 2,181 | Community | Purchased surface water |
| 25 | Nacimiento Water Company | San Luis Obispo | 2,181 | Community | Surface water |
| 26 | Golden State Water Company-Cypress Ridge | San Luis Obispo | 2,026 | Community | Groundwater |
| 27 | Avila Beach Community Services District | San Luis Obispo | 1,630 | Community | Purchased surface water |
| 28 | San Miguelito Mwc | San Luis Obispo | 1,600 | Community | Purchased surface water |
| 29 | Tiger Water Supply | San Luis Obispo | 1,600 | Non-transient non-community | Groundwater |
| 30 | Lopez Project | San Luis Obispo | 1,569 | Community | Surface water |
| 31 | County of Monterey-Lake Nacimiento | San Luis Obispo | 1,521 | Non-transient non-community | Groundwater under influence of surface water |
| 32 | Golden State Water Company - Edna | San Luis Obispo | 1,493 | Community | Groundwater |
| 33 | Caltrans - Shandon Rest Stop | San Luis Obispo | 1,300 | Transient non-community | Groundwater |
| 34 | Slo Cwwd No. 23 - Santa Margarita | San Luis Obispo | 1,291 | Community | Groundwater |
| 35 | Slocsa #10a - Cayucos | San Luis Obispo | 1,200 | Community | Purchased surface water |
| 36 | Pg&E | San Luis Obispo | 1,200 | Non-transient non-community | Surface water |
| 37 | Slo Csa No. 16 - Shandon | San Luis Obispo | 1,085 | Community | Purchased surface water |
| 38 | Daou Vineyards, LLC | San Luis Obispo | 1,025 | Non-transient non-community | Groundwater |
| 39 | Montana De Oro State Park | San Luis Obispo | 990 | Transient non-community | Surface water |
| 40 | Laureate Water Company | San Luis Obispo | 700 | Community | Groundwater |
| 41 | Coastal Christian School | San Luis Obispo | 650 | Non-transient non-community | Groundwater |
| 42 | Mesa Dunes Mobile Home Estates | San Luis Obispo | 600 | Community | Groundwater |
| 43 | S & T Mutual Water Company | San Luis Obispo | 591 | Community | Groundwater |
| 44 | Woodland Park Mutual Water Co | San Luis Obispo | 538 | Community | Groundwater |
| 45 | The Anderson | San Luis Obispo | 500 | Transient non-community | Groundwater |
| 46 | Hearst Memorial State Beach | San Luis Obispo | 500 | Transient non-community | Purchased surface water |
| 47 | Walnut Hills Mutual Water Co | San Luis Obispo | 486 | Community | Groundwater |
| 48 | San Simeon Csd | San Luis Obispo | 462 | Community | Groundwater |
| 49 | Garden Farms C.W.D. | San Luis Obispo | 440 | Community | Groundwater |
| 50 | Los Robles Mobile Home Estates | San Luis Obispo | 420 | Community | Groundwater |
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.
- Vines R.V. Resort400
- Santa Margarita Ranch Headquarters362
- Green River Mutual Water Co.350
- Santa Ysabel Ranch Mwc344
- Fiero Lane Water Company, Inc..324
- Laetitia Vineyard & Winery Inc.270
- Branch Elementary School253
- Rancho Colina Mobile Home Park252
- Cal Shasta Club240
- Parrish Family Winery207
- Jack Ready Imagination Park200
- Strasbaugh, Inc.200
- Octagon Barn Center Association200
- Sycamore Mineral Springs Resort200
- Hearst Monument State Park200
- Vachell Water System150
- Gran Cielo Mutual Water Company139
- Paso 360135
- Irish Hills Mutual Water Co135
- Canyon Crest Mutual Benefit Wc133
- Christmas Cove132
- Edna Valley Ranch East132
- San Simeon Estate Winery132
- Calipaso Winery130
- Callender Grove Mutual Water126
- J Lohr Winery125
- Port San Luis Harbor District125
- Spanish Lakes Mutual Water Co125
- Madonna Inn Water Company120
- Halcyon Water System110
- Las Ventanas Ranch108
- Paso Robles Rv Ranch105
- Varian Ranch Mutual Water105
- Pleasant Valley Elementary100
- Lopez Recreation Area100
- Creston Elementary School100
- Ragged Point Inn100
- Noll Properties100
- Resthaven Mobile Home Park99
- Le Cuvier Winery92
- Greenheart Farms91
- Pacific Dunes Ranch89
- Tri Counties Club87
- Afuera De Chorro Water Company85
- Zoo Med-Winterhaven85
- Bassi Ranch Mutual Water Co.85
- Ken Mar Gardens84
- Baron Canyon Mutual Water Co.81
- Laguna Negra Mutual Water Co.80
- Adelaida Vineyards & Winery77
- Usasa-Pom Enclave - Camp Roberts75
- Avila Valley Mutual Water Co75
- Center of Effort Winery75
- Talley Farms Labor Housing75
- Sutter Home Winery Inc.. Trinchero Cc71
- Santa Margarita Koa70
- H2o, Inc.70
- Monte Sereno Mutual Benefit Water65
- Ball Tagawa Growers60
- Country Hills Estates60
- Anza Vineyard Estates Mutual Water Co60
- Toyota San Luis Obispo57
- Booker Winery56
- Rim Rock Water Company55
- Carpenter Winery54
- Mt. Olive Organic Farm51
- Hunter Ranch Golf Course50
- Northshore S & B, Inc.50
- Paragon Triangle Water Supply50
- Laguna Vista Boat Club50
- Granite Ridge50
- Rancho Salinas Mbwc50
- Bear Valley Water Company45
- Tank Farm Business Park45
- Rancho Nipomo Water Company44
- Speedling, Inc.40
- Almira Water Association40
- Carrisa Plains Elementary40
- Elks Lodge #32240
- Jada Vineyard and Winery40
- Chamisal Vineyards40
- Slo Partners40
- Halter Ranch39
- Terra De Oro Water Company38
- Playa Dulce35
- Waste Connections Water Co35
- Parsons Water Supply35
- Guadalupe Cooling Company35
- J M Sims Water Supply34
- Horizon Lane Water Supply32
- Holdgrafer & Associates30
- Cerro Alto Campground30
- Mutual Water Association30
- Higuera Apartments30
- Caelesta Winery30
- Edna Valley Vineyards30
- Mustang Springs Mutual Water30
- Longbranch Saloon, the30
- Biddle Regional County Park27
- 141 Suburban Road Water Supply25
- Babe Ruth'S Oak View25
- Sunset Drive-in Snack Bar25
- Ada'S Lodges25
- Cuyama Lane Water Company25
- Independence Water System25
- Tmc Suburban, LLC25
- Creston Country Store25
- Precision Mutual Water Company25
- Loading Chute25
- San Paso Truck Stop25
- Paso Robles Chevrolet Cadillac25
- Congregation Beth David25
- Sixmilebridge Winery25
- Halfway Station25
- Harmony Water Works25
- Aronhill Vineyard25
- Niner Wine Estates, LLC25
- Rinconada Trailer Park10
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
- All California public water systems· 7,479 active
- San Diego County· 191 systems
- Stanislaus County· 191 systems
- Napa County· 188 systems
- Shasta County· 174 systems
- Sacramento County· 164 systems
- Santa Barbara County· 150 systems
- How to find out who supplies your drinking water
- How to find and read your annual water quality report
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).