Public water system · CA5010039
ActiveWestern Hills Water District/Diablo Gran
At a glance
Western Hills Water District/Diablo Gran (PWSID CA5010039) is an active community water system in Stanislaus County, California. It reports serving 2,000 people through 596 service connections. Its primary water source is surface water, and EPA lists it as owned by a local government. Of the 12 most recent violations in EPA's records, 7 are health-based, and the most recent began in January 2018.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
2,000
Service connections
596
Primary source
SW
Surface water
System type
CWS
Community water system
System record
How does Western Hills Water District/Diablo Gran compare with other water systems in Stanislaus County?
By EPA's size categories, Western Hills Water District/Diablo Gran is a small system (501 to 3,300 people). Stanislaus County has 191 active public water systems. Its population served is about 25% below the county average of 2,684 people per system, and accounts for 0.4% of the 512,656 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 Western Hills Water District/Diablo Gran 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. Surface water means the system draws its water from rivers, lakes, streams or reservoirs. 609 California systems (8.1%) list surface water as their primary source.
Who owns and regulates Western Hills Water District/Diablo Gran?
EPA lists Western Hills Water District/Diablo Gran 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. 57 of the 191 active systems in Stanislaus County (30%) are also owned by a local government.
Does Western Hills Water District/Diablo Gran have drinking water violations?
Of the 12 most recent violations in EPA's records, 7 are health-based, and the most recent began in January 2018. The violations listed here began between July 2009 and January 2018. By type: 7 contaminant level above the legal limit, 4 monitoring and reporting and 1 public notice, recordkeeping or other. The contaminant or rule involved most often is Total trihalomethanes (TTHM) (7 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 |
|---|---|---|---|---|
| 2018-01-01 | Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52 | Lead and Copper Rulecode 5000 | No | Resolved |
| 2017-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2016-10-01 | Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52 | Lead and Copper Rulecode 5000 | No | Resolved |
| 2016-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2016-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2016-04-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2015-10-01 | Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52 | Lead and Copper Rulecode 5000 | No | Resolved |
| 2015-01-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2014-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2014-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Total trihalomethanes (TTHM)code 2950 | Yes | Resolved |
| 2009-10-01 | Monitoring and reportingMonitoring and Reporting (DBP) · code 27 | Carbon, totalcode 2920 | No | Resolved |
| 2009-07-01 | Public notice, recordkeeping or otherConsumer Confidence Report Complete Failure to Report · code 71 | Consumer Confidence Rulecode 7000 | No | 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.
Western Hills Water District/Diablo Gran: frequently asked questions
Who runs Western Hills Water District/Diablo Gran?
Western Hills Water District/Diablo Gran (PWSID CA5010039) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does Western Hills Water District/Diablo Gran serve?
Western Hills Water District/Diablo Gran reports serving 2,000 people through 596 service connections in Stanislaus County, California.
Where does Western Hills Water District/Diablo Gran get its water?
EPA SDWIS lists this system's primary water source as surface water. Surface water means the system draws its water from rivers, lakes, streams or reservoirs.
Does Western Hills Water District/Diablo Gran have any drinking water violations?
Of the 12 most recent violations in EPA's records, 7 are health-based, and the most recent began in January 2018. 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 Western Hills Water District/Diablo Gran'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, 7 are health-based, and the most recent began in January 2018. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find Western Hills Water District/Diablo Gran's water quality report?
As a community water system, Western Hills Water District/Diablo Gran 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 Stanislaus County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Modesto, City of | Stanislaus | 218,771 | Community | Purchased surface water |
| Turlock, City of | Stanislaus | 72,682 | Community | Purchased surface water |
| Ceres, City of | Stanislaus | 54,513 | Community | Purchased surface water |
| Patterson, City of | Stanislaus | 24,977 | Community | Groundwater |
| Riverbank, City of | Stanislaus | 24,834 | Community | Groundwater |
| Oakdale, City of | Stanislaus | 23,235 | 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, “Western Hills Water District/Diablo Gran, PWSID CA5010039, California”, https://aquacensus.com/water-systems/california/western-hills-water-district-diablo-gran-ca5010039 (data as of October 1, 2026).