Public water system · CA4110001
ActiveMid-Peninsula Water District
At a glance
Mid-Peninsula Water District (PWSID CA4110001) is an active community water system in San Mateo County, California. It reports serving 30,609 people through 8,179 service connections. Its primary water source is purchased surface water, and EPA lists it as owned by a local government. EPA's records list 3 violations for this system; all are health-based, and the most recent began in March 2015.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
30,609
Service connections
8,179
Primary source
SWP
Purchased surface water
System type
CWS
Community water system
System record
How does Mid-Peninsula Water District compare with other water systems in San Mateo County?
By EPA's size categories, Mid-Peninsula 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 twice the county average of 15,363 people per system, and accounts for 3.9% 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 Mid-Peninsula Water District is about 4.6 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. 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 Mid-Peninsula Water District?
EPA lists Mid-Peninsula 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 Mid-Peninsula Water District have drinking water violations?
EPA's records list 3 violations for this system; all are health-based, and the most recent began in March 2015. The violations listed here began between December 2001 and March 2015. By type: 2 contaminant level above the legal limit and 1 required treatment not met. The contaminant or rule involved most often is Total coliform bacteria (TCR) (2 of them). EPA lists 3 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 |
|---|---|---|---|---|
| 2015-03-01 | Required treatment not metTreatment Technique (SWTR and GWR) · code 41 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2002-12-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2001-12-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
All 3 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.
Mid-Peninsula Water District: frequently asked questions
Who runs Mid-Peninsula Water District?
Mid-Peninsula Water District (PWSID CA4110001) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does Mid-Peninsula Water District serve?
Mid-Peninsula Water District reports serving 30,609 people through 8,179 service connections in San Mateo County, California.
Where does Mid-Peninsula 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 Mid-Peninsula Water District have any drinking water violations?
EPA's records list 3 violations for this system; all are health-based, and the most recent began in March 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 Mid-Peninsula 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 3 violations for this system; all are health-based, and the most recent began in March 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 Mid-Peninsula Water District's water quality report?
As a community water system, Mid-Peninsula 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, “Mid-Peninsula Water District, PWSID CA4110001, California”, https://aquacensus.com/water-systems/california/mid-peninsula-water-district-ca4110001 (data as of October 1, 2026).