Public water system · CA4110027
ActiveWestborough Water District
At a glance
Westborough Water District (PWSID CA4110027) is an active community water system in San Mateo County, California. It reports serving 13,486 people through 3,907 service connections. Its primary water source is purchased surface water, and EPA lists it as owned by a local government. EPA's records list 2 violations for this system; all are health-based, and the most recent began in July 1998.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
13,486
Service connections
3,907
Primary source
SWP
Purchased surface water
System type
CWS
Community water system
System record
How does Westborough Water District compare with other water systems in San Mateo County?
By EPA's size categories, Westborough Water District is a large system (10,001 to 100,000 people). San Mateo County has 51 active public water systems. Its population served is about 12% below the county average of 15,363 people per system, and accounts for 1.7% 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 Westborough Water District is about twice 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. Purchased surface water means the system buys surface water from another public water system rather than drawing its own. 506 California systems (6.8%) list purchased surface water as their primary source.
Who owns and regulates Westborough Water District?
EPA lists Westborough Water District 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 Westborough Water District have drinking water violations?
EPA's records list 2 violations for this system; all are health-based, and the most recent began in July 1998. The violations listed here began between October 1991 and July 1998. By type: 1 contaminant level above the legal limit and 1 required treatment not met. The contaminants or rules involved are Total coliform bacteria (TCR) and Surface Water Treatment Rule. EPA lists 2 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 |
|---|---|---|---|---|
| 1998-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1991-10-01 | Required treatment not metTreatment Technique (SWTR and GWR) · code 41 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
All 2 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.
Westborough Water District: frequently asked questions
Who runs Westborough Water District?
Westborough Water District (PWSID CA4110027) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does Westborough Water District serve?
Westborough Water District reports serving 13,486 people through 3,907 service connections in San Mateo County, California.
Where does Westborough Water District get its water?
EPA SDWIS lists this system's primary water source as purchased surface water. Purchased surface water means the system buys surface water from another public water system rather than drawing its own.
Does Westborough Water District have any drinking water violations?
EPA's records list 2 violations for this system; all are health-based, and the most recent began in July 1998. 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 Westborough Water District'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 2 violations for this system; all are health-based, and the most recent began in July 1998. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find Westborough Water District's water quality report?
As a community water system, Westborough Water District 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, “Westborough Water District, PWSID CA4110027, California”, https://aquacensus.com/water-systems/california/westborough-water-district-ca4110027 (data as of October 1, 2026).