Public water system · CA4901156
ActiveWillowside School
At a glance
Willowside School (PWSID CA4901156) is an active non-transient non-community water system in Sonoma County, California. It reports serving 460 people through 5 service connections. Its primary water source is groundwater, and EPA lists it as owned by a local government. EPA's records list 4 violations for this system; 2 are health-based, and the most recent began in October 2024.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
460
Service connections
5
Primary source
GW
Groundwater
System type
NTNCWS
Non-transient non-community water system
System record
How does Willowside School compare with other water systems in Sonoma County?
By EPA's size categories, Willowside School is a very small system (500 people or fewer). Sonoma County has 441 active public water systems. Its population served is about 58% 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 non-transient non-community water system reports serving 430 people, so Willowside School is roughly in line with that figure.
What does “non-transient non-community water system” mean?
A non-transient non-community water system regularly serves at least 25 of the same people for more than six months a year, but not where they live. Schools, factories, office buildings and hospitals with their own supply are typical examples. California has 1,466 active non-transient non-community water systems, 20% 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 Willowside School?
EPA lists Willowside School 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 Willowside School have drinking water violations?
EPA's records list 4 violations for this system; 2 are health-based, and the most recent began in October 2024. The violations listed here began between November 1994 and October 2024. By type: 1 reporting, 1 required treatment not met, 1 contaminant level above the legal limit and 1 monitoring and reporting. The contaminant or rule involved most often is Lead and Copper Rule Revisions (2 of them). EPA lists 2 as unaddressed and 2 as resolved. Unaddressed means the violation is not resolved or archived and is not yet covered by formal enforcement. 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 |
|---|---|---|---|---|
| 2024-10-17 | ReportingLSL Reporting · code 4G | Lead and Copper Rule Revisionscode 5200 | No | Unaddressed |
| 2024-10-17 | Required treatment not metLSL Inventory · code 2E | Lead and Copper Rule Revisionscode 5200 | Yes | Unaddressed |
| 1996-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1994-11-01 | Monitoring and reportingMonitoring, Repeat Major (TCR) · code 25 | Total coliform bacteria (TCR)code 3100 | No | 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.
Willowside School: frequently asked questions
Who runs Willowside School?
Willowside School (PWSID CA4901156) is a non-transient non-community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does Willowside School serve?
Willowside School reports serving 460 people through 5 service connections in Sonoma County, California.
Where does Willowside School 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 Willowside School have any drinking water violations?
EPA's records list 4 violations for this system; 2 are health-based, and the most recent began in October 2024. 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 Willowside School'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; 2 are health-based, and the most recent began in October 2024. For current results, consult EPA ECHO, or the CA state drinking water program.
Where can I find Willowside School's water quality report?
The annual Consumer Confidence Report requirement applies to community water systems. Willowside School is a non-transient non-community water system, so it is not required to publish one; like every public water system, it must notify the people it serves about violations under EPA's public notification rules.
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, “Willowside School, PWSID CA4901156, California”, https://aquacensus.com/water-systems/california/willowside-school-ca4901156 (data as of October 1, 2026).