Public water system · CA4900640
ActiveSonoma County Mutual Water Company
At a glance
Sonoma County Mutual Water Company (PWSID CA4900640) is an active community water system in Sonoma County, California. It reports serving 40 people through 18 service connections. Its primary water source is groundwater under influence of 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 July 2020.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
40
Service connections
18
Primary source
GU
Groundwater under influence of surface water
System type
CWS
Community water system
System record
How does Sonoma County Mutual Water Company compare with other water systems in Sonoma County?
By EPA's size categories, Sonoma County Mutual Water Company is a very small system (500 people or fewer). Sonoma County has 441 active public water systems. Its population served is well below the county average of 1,092 people per system, and accounts for less than 0.1% of the 481,435 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 Sonoma County Mutual Water Company 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. Groundwater under the influence of surface water is well or spring water that the regulator has found to be affected by nearby surface water, so it is regulated under the surface-water treatment rules. 105 California systems (1.4%) list groundwater under influence of surface water as their primary source.
Who owns and regulates Sonoma County Mutual Water Company?
EPA lists Sonoma County Mutual Water Company 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. 371 of the 441 active systems in Sonoma County (84%) are also privately owned.
Does Sonoma County Mutual Water Company have drinking water violations?
Of the 12 most recent violations in EPA's records, 12 are health-based, and the most recent began in July 2020. The violations listed here began between October 2018 and July 2020. By type: 12 required treatment not met. The contaminant or rule involved most often is Surface Water Treatment Rule (12 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 |
|---|---|---|---|---|
| 2020-07-23 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2019-08-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2019-07-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2019-06-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2019-05-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2019-04-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2019-03-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2019-02-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2019-01-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2018-12-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2018-11-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
| 2018-10-01 | Required treatment not metFailure to Filter (SWTR) · code 42 | Surface Water Treatment Rulecode 0200 | 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.
Sonoma County Mutual Water Company: frequently asked questions
Who runs Sonoma County Mutual Water Company?
Sonoma County Mutual Water Company (PWSID CA4900640) is a community water system privately owned. It is regulated by the CA state drinking water program.
How many people does Sonoma County Mutual Water Company serve?
Sonoma County Mutual Water Company reports serving 40 people through 18 service connections in Sonoma County, California.
Where does Sonoma County Mutual Water Company get its water?
EPA SDWIS lists this system's primary water source as groundwater under influence of surface water. Groundwater under the influence of surface water is well or spring water that the regulator has found to be affected by nearby surface water, so it is regulated under the surface-water treatment rules.
Does Sonoma County Mutual Water Company 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 July 2020. 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 Sonoma County Mutual Water Company'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 July 2020. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find Sonoma County Mutual Water Company's water quality report?
As a community water system, Sonoma County Mutual Water Company 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 Sonoma County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Santa Rosa, City of | Sonoma | 175,396 | Community | Groundwater |
| Petaluma, City of | Sonoma | 60,781 | Community | Groundwater |
| Rohnert Park, City of | Sonoma | 43,821 | Community | Groundwater |
| Windsor, Town of | Sonoma | 25,561 | Community | Groundwater |
| Valley of the Moon Water District | Sonoma | 23,107 | Community | Groundwater |
| Sonoma, City of | Sonoma | 11,725 | 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, “Sonoma County Mutual Water Company, PWSID CA4900640, California”, https://aquacensus.com/water-systems/california/sonoma-county-mutual-water-company-ca4900640 (data as of October 1, 2026).