Public water system · CA2210924
ActiveYosemite West Water System
At a glance
Yosemite West Water System (PWSID CA2210924) is an active community water system in Mariposa County, California. It reports serving 420 people through 185 service connections. Its primary water source is groundwater, and EPA lists it as owned by a local government. Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in October 2025.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
420
Service connections
185
Primary source
GW
Groundwater
System type
CWS
Community water system
System record
How does Yosemite West Water System compare with other water systems in Mariposa County?
By EPA's size categories, Yosemite West Water System is a very small system (500 people or fewer). Mariposa County has 67 active public water systems. Its population served is about 10% above the county average of 381 people per system, and accounts for 1.6% of the 25,508 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 Yosemite West Water System 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 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 Yosemite West Water System?
EPA lists Yosemite West Water System 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. 21 of the 67 active systems in Mariposa County (31%) are also owned by a local government.
Does Yosemite West Water System have drinking water violations?
Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in October 2025. The violations listed here began between December 1996 and October 2025. By type: 6 monitoring and reporting and 6 contaminant level above the legal limit. The contaminant or rule involved most often is Total coliform bacteria (TCR) (7 of them). EPA lists 11 as resolved and 1 as addressed. 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. Addressed means the violation is not resolved or archived and is covered by formal enforcement.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2025-10-01 | Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52 | Lead and Copper Rulecode 5000 | No | Addressed |
| 2012-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
| 2011-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2010-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2009-09-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2008-09-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2006-02-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 2004-03-01 | Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52 | Lead and Copper Rulecode 5000 | No | Resolved |
| 2003-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
| 2002-06-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2001-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitratecode 1040 | No | Resolved |
| 1996-12-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | 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.
Yosemite West Water System: frequently asked questions
Who runs Yosemite West Water System?
Yosemite West Water System (PWSID CA2210924) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does Yosemite West Water System serve?
Yosemite West Water System reports serving 420 people through 185 service connections in Mariposa County, California.
Where does Yosemite West Water System 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 Yosemite West Water System have any drinking water violations?
Of the 12 most recent violations in EPA's records, 6 are health-based, and the most recent began in October 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 Yosemite West Water System'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, 6 are health-based, and the most recent began in October 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 Yosemite West Water System's water quality report?
As a community water system, Yosemite West Water System 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 Mariposa County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Yosemite Nps-Glacier Point | Mariposa | 4,000 | Transient non-community | Surface water |
| Blm-Briceburg Water System | Mariposa | 3,196 | Transient non-community | Groundwater |
| Mariposa Public Utility Dist | Mariposa | 2,000 | Community | Surface water |
| Yosemite Nps-Bridalveil Fall | Mariposa | 1,163 | Transient non-community | Groundwater |
| Mid - Mc Swain Rec Area | Mariposa | 1,119 | Transient non-community | Surface water |
| Yosemite Nps-Yosemite Valley | Mariposa | 1,000 | 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, “Yosemite West Water System, PWSID CA2210924, California”, https://aquacensus.com/water-systems/california/yosemite-west-water-system-ca2210924 (data as of October 1, 2026).