Public water system · CA4110010
ActiveMontara Water and Sanitary District
At a glance
Montara Water and Sanitary District (PWSID CA4110010) is an active community water system in San Mateo County, California. It reports serving 6,078 people through 1,698 service connections. Its primary water source is surface water, and EPA lists it as owned by a local government. EPA's records list 4 violations for this system; 3 are health-based, and the most recent began in June 2010.
This page covers its drinking water system only; sewer and wastewater service are not part of EPA's drinking water records.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
6,078
Service connections
1,698
Primary source
SW
Surface water
System type
CWS
Community water system
System record
How does Montara Water and Sanitary District compare with other water systems in San Mateo County?
By EPA's size categories, Montara Water and Sanitary District is a medium system (3,301 to 10,000 people). San Mateo County has 51 active public water systems. Its population served is about 60% below the county average of 15,363 people per system, and accounts for 0.8% 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 Montara Water and Sanitary District is roughly in line with 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 Montara Water and Sanitary District?
EPA lists Montara Water and Sanitary 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 Montara Water and Sanitary District have drinking water violations?
EPA's records list 4 violations for this system; 3 are health-based, and the most recent began in June 2010. The violations listed here began between February 1996 and June 2010. By type: 3 contaminant level above the legal limit and 1 monitoring and reporting. The contaminant or rule involved most often is Nitrate (2 of them). EPA lists 4 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 |
|---|---|---|---|---|
| 2010-06-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Single Sample · code 01 | Nitratecode 1040 | Yes | Resolved |
| 1996-12-31 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Single Sample · code 01 | Cyanidecode 1024 | Yes | Resolved |
| 1996-12-31 | Monitoring and reportingMonitoring, Check/Repeat/Confirmation · code 04 | Nitratecode 1040 | No | Resolved |
| 1996-02-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
All 4 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.
Montara Water and Sanitary District: frequently asked questions
Who runs Montara Water and Sanitary District?
Montara Water and Sanitary District (PWSID CA4110010) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does Montara Water and Sanitary District serve?
Montara Water and Sanitary District reports serving 6,078 people through 1,698 service connections in San Mateo County, California.
Where does Montara Water and Sanitary District 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 Montara Water and Sanitary District have any drinking water violations?
EPA's records list 4 violations for this system; 3 are health-based, and the most recent began in June 2010. 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 Montara Water and Sanitary 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 4 violations for this system; 3 are health-based, and the most recent began in June 2010. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find Montara Water and Sanitary District's water quality report?
As a community water system, Montara Water and Sanitary 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, “Montara Water and Sanitary District, PWSID CA4110010, California”, https://aquacensus.com/water-systems/california/montara-water-and-sanitary-district-ca4110010 (data as of October 1, 2026).