Public water system · CA4010009
ActiveSan Luis Obispo Water Department
At a glance
San Luis Obispo Water Department (PWSID CA4010009) is an active community water system in San Luis Obispo County, California. It reports serving 47,788 people through 17,012 service connections. Its primary water source is surface water, and EPA lists it as owned by a local government. EPA's records list one violation for this system; it is health-based, and the most recent began in April 2015.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
47,788
Service connections
17,012
Primary source
SW
Surface water
System type
CWS
Community water system
System record
How does San Luis Obispo Water Department compare with other water systems in San Luis Obispo County?
By EPA's size categories, San Luis Obispo Water Department is a large system (10,001 to 100,000 people). San Luis Obispo County has 171 active public water systems, and San Luis Obispo Water Department is the 2nd-largest of them by population served. Its population served is about 23 times the county average of 2,038 people per system, and accounts for 14% of the 348,510 people reported by systems filed under the county. Across California, the 7,479 active systems average 5,706 people each. Nationally, the average active community water system reports serving 6,703 people, so San Luis Obispo Water Department is about 7.1 times that figure.
What does “community water system” mean?
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. California has 2,997 active community water systems, 40% of the state's 7,479 active systems. Surface water means the system draws its water from rivers, lakes, streams or reservoirs. 609 California systems (8.1%) list surface water as their primary source.
Who owns and regulates San Luis Obispo Water Department?
EPA lists San Luis Obispo Water Department as owned by a local government. The CA state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 33 of the 171 active systems in San Luis Obispo County (19%) are also owned by a local government.
Does San Luis Obispo Water Department have drinking water violations?
EPA's records list one violation for this system; it is health-based, and the most recent began in April 2015. By type: 1 contaminant level above the legal limit. The contaminant or rule involved is Total trihalomethanes (TTHM). EPA lists 1 as resolved. Resolved means at least one resolving action is on record: the system returned to compliance, the rule no longer applies, or no further action was needed.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2015-04-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
The one violation in EPA's records.Labels and codes come from EPA's SDWIS reference tables. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found. "Health-based" marks violations of a legal limit or required treatment.
San Luis Obispo Water Department: frequently asked questions
Who runs San Luis Obispo Water Department?
San Luis Obispo Water Department (PWSID CA4010009) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does San Luis Obispo Water Department serve?
San Luis Obispo Water Department reports serving 47,788 people through 17,012 service connections in San Luis Obispo County, California.
Where does San Luis Obispo Water Department get its water?
EPA SDWIS lists this system's primary water source as surface water. Surface water means the system draws its water from rivers, lakes, streams or reservoirs.
Does San Luis Obispo Water Department have any drinking water violations?
EPA's records list one violation for this system; it is health-based, and the most recent began in April 2015. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found.
Is San Luis Obispo Water Department's water safe to drink?
AquaCensus shows EPA compliance records, not current water test results, so it cannot say whether the water is safe at a given moment. EPA's records list one violation for this system; it is health-based, and the most recent began in April 2015. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find San Luis Obispo Water Department's water quality report?
As a community water system, San Luis Obispo Water Department must deliver an annual water quality report, called a Consumer Confidence Report, to its customers by July 1 each year, covering the previous calendar year. The system can provide a copy on request.
Other water systems in San Luis Obispo County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Santa Margarita Recreation Area | San Luis Obispo | 50,001 | Transient non-community | Groundwater |
| City of Paso Robles Water Division | San Luis Obispo | 31,176 | Community | Surface water |
| Atascadero Mutual Water Co | San Luis Obispo | 30,618 | Community | Groundwater |
| City of Arroyo Grande Utilities Division | San Luis Obispo | 17,963 | Community | Purchased surface water |
| California Mens Colony | San Luis Obispo | 15,000 | Community | Surface water |
| Nipomo Comm Services Dist | San Luis Obispo | 13,771 | Community | Purchased surface water |
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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, “San Luis Obispo Water Department, PWSID CA4010009, California”, https://aquacensus.com/water-systems/california/san-luis-obispo-water-department-ca4010009 (data as of October 1, 2026).