Public water system · CA4100509
ActiveCounty Service Area 7
At a glance
County Service Area 7 (PWSID CA4100509) is an active community water system in San Mateo County, California. It reports serving 300 people through 68 service connections. Its primary water source is surface water, and EPA lists it as owned by a local government. Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in January 2025.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
300
Service connections
68
Primary source
SW
Surface water
System type
CWS
Community water system
System record
How does County Service Area 7 compare with other water systems in San Mateo County?
By EPA's size categories, County Service Area 7 is a very small system (500 people or fewer). San Mateo County has 51 active public water systems. Its population served is well below the county average of 15,363 people per system, and accounts for less than 0.1% of the 783,522 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 County Service Area 7 is well below 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 County Service Area 7?
EPA lists County Service Area 7 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. 19 of the 51 active systems in San Mateo County (37%) are also owned by a local government.
Does County Service Area 7 have drinking water violations?
Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in January 2025. The violations listed here began between January 2004 and January 2025. By type: 6 contaminant level above the legal limit and 6 monitoring and reporting. The contaminant or rule involved most often is Total trihalomethanes (TTHM) (4 of them). EPA lists 12 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 |
|---|---|---|---|---|
| 2025-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Haloacetic acids (HAA5)code 2456 | Yes | Resolved |
| 2020-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Haloacetic acids (HAA5)code 2456 | Yes | Resolved |
| 2018-04-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2018-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2017-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2017-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2004-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Xylenes, Totalcode 2955 | No | Resolved |
| 2004-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Carbon tetrachloridecode 2982 | No | Resolved |
| 2004-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Ethylbenzenecode 2992 | No | Resolved |
| 2004-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Benzenecode 2990 | No | Resolved |
| 2004-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Toluenecode 2991 | No | Resolved |
| 2004-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Chlorobenzenecode 2989 | No | Resolved |
The 12 most recent violations in EPA's records, newest first.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.
County Service Area 7: frequently asked questions
Who runs County Service Area 7?
County Service Area 7 (PWSID CA4100509) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does County Service Area 7 serve?
County Service Area 7 reports serving 300 people through 68 service connections in San Mateo County, California.
Where does County Service Area 7 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 County Service Area 7 have any drinking water violations?
Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in January 2025. 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 County Service Area 7'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. Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in January 2025. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find County Service Area 7's water quality report?
As a community water system, County Service Area 7 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 Mateo County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| City of Daly City | San Mateo | 104,901 | Community | Purchased surface water |
| California Water Service - San Mateo | San Mateo | 102,348 | Community | Purchased surface water |
| City of Redwood City | San Mateo | 92,819 | Community | Purchased surface water |
| California Water Service-S San Francisco | San Mateo | 64,146 | Community | Purchased surface water |
| California Water Service - Bear Gulch | San Mateo | 61,431 | Community | Surface water |
| City of San Bruno | San Mateo | 42,631 | 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, “County Service Area 7, PWSID CA4100509, California”, https://aquacensus.com/water-systems/california/county-service-area-7-ca4100509 (data as of October 1, 2026).