Public water system · CA5610702
ActiveU.S.N., San Nicolas Island
At a glance
U.S.N., San Nicolas Island (PWSID CA5610702) is an active community water system in Ventura County, California. It reports serving 254 people through 106 service connections. Its primary water source is groundwater under influence of surface water, and EPA lists it as owned by the federal government. EPA's records list 11 violations for this system; 4 are health-based, and the most recent began in December 2012.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
254
Service connections
106
Primary source
GU
Groundwater under influence of surface water
System type
CWS
Community water system
System record
How does U.S.N., San Nicolas Island compare with other water systems in Ventura County?
By EPA's size categories, U.S.N., San Nicolas Island is a very small system (500 people or fewer). Ventura County has 95 active public water systems. Its population served is well below the county average of 9,293 people per system, and accounts for less than 0.1% of the 882,799 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 U.S.N., San Nicolas Island 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 U.S.N., San Nicolas Island?
EPA lists U.S.N., San Nicolas Island as owned by the federal 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. 6 of the 95 active systems in Ventura County (6.3%) are also owned by the federal government.
Does U.S.N., San Nicolas Island have drinking water violations?
EPA's records list 11 violations for this system; 4 are health-based, and the most recent began in December 2012. The violations listed here began between July 1993 and December 2012. By type: 7 monitoring and reporting, 3 contaminant level above the legal limit and 1 required treatment not met. The contaminant or rule involved most often is Total coliform bacteria (TCR) (8 of them). EPA lists 11 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 |
|---|---|---|---|---|
| 2012-12-01 | Monitoring and reportingMonitoring of Treatment (SWTR-Filter) · code 36 | Surface Water Treatment Rulecode 0200 | No | Resolved |
| 2005-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2003-12-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2003-07-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 2001-12-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 2000-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2000-04-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1998-02-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1997-11-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1995-12-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1993-07-01 | Required treatment not metTreatment Technique (SWTR and GWR) · code 41 | Surface Water Treatment Rulecode 0200 | Yes | Resolved |
All 11 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.
U.S.N., San Nicolas Island: frequently asked questions
Who runs U.S.N., San Nicolas Island?
U.S.N., San Nicolas Island (PWSID CA5610702) is a community water system owned by the federal government. It is regulated by the CA state drinking water program.
How many people does U.S.N., San Nicolas Island serve?
U.S.N., San Nicolas Island reports serving 254 people through 106 service connections in Ventura County, California.
Where does U.S.N., San Nicolas Island 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 U.S.N., San Nicolas Island have any drinking water violations?
EPA's records list 11 violations for this system; 4 are health-based, and the most recent began in December 2012. 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 U.S.N., San Nicolas Island'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 11 violations for this system; 4 are health-based, and the most recent began in December 2012. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find U.S.N., San Nicolas Island's water quality report?
As a community water system, U.S.N., San Nicolas Island 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 Ventura County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Oxnard Water Dept | Ventura | 200,232 | Community | Purchased surface water |
| Ventura Water Department | Ventura | 113,500 | Community | Surface water |
| Ventura Wwd No. 8 - Simi Valley | Ventura | 94,738 | Community | Purchased surface water |
| Cal American Water Co | Ventura | 66,809 | Community | Purchased surface water |
| City of Thousand Oaks Water Department | Ventura | 53,157 | Community | Purchased surface water |
| Camarillo Water Dept | Ventura | 46,824 | 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, “U.S.N., San Nicolas Island, PWSID CA5610702, California”, https://aquacensus.com/water-systems/california/u-s-n-san-nicolas-island-ca5610702 (data as of October 1, 2026).