Public water system · CA2100519
ActiveEstero Mutual
At a glance
Estero Mutual (PWSID CA2100519) is an active community water system in Marin County, California. It reports serving 206 people through 148 service connections. Its primary water source is surface water, and EPA lists it as privately owned. Of the 12 most recent violations in EPA's records, 12 are health-based, and the most recent began in October 2021.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
206
Service connections
148
Primary source
SW
Surface water
System type
CWS
Community water system
System record
How does Estero Mutual compare with other water systems in Marin County?
By EPA's size categories, Estero Mutual is a very small system (500 people or fewer). Marin County has 46 active public water systems. Its population served is well below the county average of 6,203 people per system, and accounts for less than 0.1% of the 285,353 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 Estero Mutual 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 Estero Mutual?
EPA lists Estero Mutual as privately owned. 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. 22 of the 46 active systems in Marin County (48%) are also privately owned.
Does Estero Mutual have drinking water violations?
Of the 12 most recent violations in EPA's records, 12 are health-based, and the most recent began in October 2021. The violations listed here began between January 2014 and October 2021. By type: 12 contaminant level above the legal limit. The contaminant or rule involved most often is Total trihalomethanes (TTHM) (11 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 |
|---|---|---|---|---|
| 2021-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2021-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2016-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2016-04-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2016-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2015-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2015-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2015-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2015-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Haloacetic acids (HAA5)code 2456 | Yes | Resolved |
| 2014-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2014-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2014-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | 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.
Estero Mutual: frequently asked questions
Who runs Estero Mutual?
Estero Mutual (PWSID CA2100519) is a community water system privately owned. It is regulated by the CA state drinking water program.
How many people does Estero Mutual serve?
Estero Mutual reports serving 206 people through 148 service connections in Marin County, California.
Where does Estero Mutual 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 Estero Mutual have any drinking water violations?
Of the 12 most recent violations in EPA's records, 12 are health-based, and the most recent began in October 2021. 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 Estero Mutual'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, 12 are health-based, and the most recent began in October 2021. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find Estero Mutual's water quality report?
As a community water system, Estero Mutual 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 Marin County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Marin Municipal Water District | Marin | 186,895 | Community | Surface water |
| North Marin Water District | Marin | 61,691 | Community | Surface water |
| Nps Ggnra | Marin | 18,447 | Community | Purchased surface water |
| Bolinas Community PUD | Marin | 2,483 | Community | Surface water |
| North Marin Wd - Pt. Reyes | Marin | 1,841 | Community | Groundwater |
| Csp - Angel Island St Park | Marin | 1,622 | Transient non-community | Groundwater |
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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, “Estero Mutual, PWSID CA2100519, California”, https://aquacensus.com/water-systems/california/estero-mutual-ca2100519 (data as of October 1, 2026).