Public water system · CA4910012
ActiveSonoma, City of
At a glance
City of Sonoma (PWSID CA4910012) is an active community water system in Sonoma County, California. It reports serving 11,725 people through 4,343 service connections. Its primary water source is groundwater, and EPA lists it as owned by a local government. EPA's records list 9 violations for this system; 1 is health-based, and the most recent began in July 2025.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
11,725
Service connections
4,343
Primary source
GW
Groundwater
System type
CWS
Community water system
System record
How does City of Sonoma compare with other water systems in Sonoma County?
By EPA's size categories, City of Sonoma is a large system (10,001 to 100,000 people). Sonoma County has 441 active public water systems, and City of Sonoma is the 6th-largest of them by population served. Its population served is about 11 times the county average of 1,092 people per system, and accounts for 2.4% 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 City of Sonoma is about 75% above 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 means the system draws its water from wells or springs fed by underground aquifers. 6,179 California systems (83%) list groundwater as their primary source.
Who owns and regulates City of Sonoma?
EPA lists City of Sonoma 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. 58 of the 441 active systems in Sonoma County (13%) are also owned by a local government.
Does City of Sonoma have drinking water violations?
EPA's records list 9 violations for this system; 1 is health-based, and the most recent began in July 2025. The violations listed here began between January 2006 and July 2025. By type: 6 monitoring and reporting, 1 reporting, 1 monitoring and 1 contaminant level above the legal limit. The contaminant or rule involved most often is Haloacetic acids (HAA5) (2 of them). EPA lists 8 as resolved and 1 as unaddressed. 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. Unaddressed means the violation is not resolved or archived and is not yet covered by formal enforcement.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2025-07-02 | ReportingNotification, Known or Potential LSL · code 4H | Lead and Copper Rule Revisionscode 5200 | No | Unaddressed |
| 2021-04-01 | Monitoring and reportingMonitoring, Regular · code 03 | Arseniccode 1005 | No | Resolved |
| 2020-01-01 | Monitoring and reportingMonitoring, Routine (IDSE) · code 30 | Haloacetic acids (HAA5)code 2456 | No | Resolved |
| 2020-01-01 | Monitoring and reportingMonitoring, Routine (IDSE) · code 30 | Total trihalomethanes (TTHM)code 2950 | No | Resolved |
| 2017-11-01 | MonitoringMonitoring, Routine (RTCR) · code 3A | Revised Total Coliform Rulecode 8000 | No | Resolved |
| 2010-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2006-04-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Total trihalomethanes (TTHM)code 2950 | No | Resolved |
| 2006-04-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Haloacetic acids (HAA5)code 2456 | No | Resolved |
| 2006-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
All 9 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.
City of Sonoma: frequently asked questions
Who runs City of Sonoma?
City of Sonoma (PWSID CA4910012) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does City of Sonoma serve?
City of Sonoma reports serving 11,725 people through 4,343 service connections in Sonoma County, California.
Where does City of Sonoma get its water?
EPA SDWIS lists this system's primary water source as groundwater. Groundwater means the system draws its water from wells or springs fed by underground aquifers.
Does City of Sonoma have any drinking water violations?
EPA's records list 9 violations for this system; 1 is health-based, and the most recent began in July 2025. 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 City of Sonoma'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 9 violations for this system; 1 is health-based, and the most recent began in July 2025. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find City of Sonoma's water quality report?
As a community water system, City of Sonoma 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 State University | Sonoma | 10,986 | Community | Groundwater |
Related pages
Working with water-system records? Pro adds alerts, change history and CSV export ($49/mo); Enterprise adds full national files, the API and an MCP server for AI tools.
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, City of, PWSID CA4910012, California”, https://aquacensus.com/water-systems/california/sonoma-city-of-ca4910012 (data as of October 1, 2026).