WESTERN HILLS WATER DISTRICT/DIABLO GRAN
PWS ID: CA5010039 · PATTERSON, California 95363
WESTERN HILLS WATER DISTRICT/DIABLO GRAN serves 2,000 people in PATTERSON, California using Surface Water water sources. It has 87 recorded EPA violations, including 62 health-based violations. No PFAS contamination was detected in UCMR5 testing.
Water Quality Snapshot: WESTERN HILLS WATER DISTRICT/DIABLO GRAN
WESTERN HILLS WATER DISTRICT/DIABLO GRAN is a local-owned community water system that delivers drinking water to 2,000 residents in PATTERSON, California (Stanislaus County) through 596 service connections. Its water is drawn from surface water sources. EPA's Safe Drinking Water Information System records 87 total violations for this system , of which 62 (71%) are health-based — meaning a contaminant exceeded an EPA Maximum Contaminant Level or a required treatment technique failed. A further 19 monitoring and reporting violations are on file. The most recent violation on record dates to 2018.
The most frequently cited contaminant at this system is TTHM, recorded in 46 violations (MCL, health-based). This system has not yet been sampled under EPA's UCMR5 PFAS monitoring program, so no PFAS detection data is available here.
Across California, EPA tracks 7,249 public water systems serving 42,404,883 people, with 153,308 cumulative violations and 63,983 health-based violations on record. About 89% of systems in the state carry at least one violation, and state-wide the average per system is 21.1 violations. WESTERN HILLS WATER DISTRICT/DIABLO GRAN's 87 violations sit above the California average. Statewide, 447 of 694 UCMR5-tested systems have reported PFAS detections (64.4%). All figures above are sourced directly from EPA SDWIS and UCMR5 public data releases and are updated as EPA publishes new reporting cycles.
System Details
- System Type
- Community
- Owner Type
- Local
- Connections
- 596
- County
- Stanislaus
- School/Daycare
- No
- MCL Violations
- 60
- Monitoring Violations
- 19
- Treatment Tech Violations
- 2
Violation History
Contaminant violations recorded by EPA.
| Contaminant | Category | Count | Latest |
|---|---|---|---|
| TTHM | MCL | 46 | 2017 |
| Total Haloacetic Acids (HAA5) | MCL | 14 | 2006 |
| Coliform (TCR) | MR | 7 | 2008 |
| Lead and Copper Rule | MR | 6 | 2018 |
| Surface Water Treatment Rule | MR | 4 | 2008 |
| Consumer Confidence Rule | Other | 3 | 2009 |
| CARBON, TOTAL | MR | 2 | 2009 |
| Surface Water Treatment Rule | TT | 2 | 2006 |
Verify This Water System
The figures above are aggregated from EPA's public databases. To verify the underlying records — or to file a complaint, request a Consumer Confidence Report, or check current monitoring status — go directly to the federal and state regulators that enforce the Safe Drinking Water Act for WESTERN HILLS WATER DISTRICT/DIABLO GRAN.
EPA SDWIS — Federal Reports
EPA's Safe Drinking Water Information System (SDWIS) holds the federal compliance record for every regulated public water system. Open the system-level report by PWS ID:
View PWS ID CA5010039 on SDWISSource: EPA SDWIS Federal Reports Search
California Drinking Water Authority
California State Water Resources Control Board — Division of Drinking Water is the primacy agency that licenses and inspects WESTERN HILLS WATER DISTRICT/DIABLO GRAN under EPA-delegated authority.
Open CA regulator portalSource: California State Water Resources Control Board — Division of Drinking Water
Violation Timeline
Each row links to the EPA SDWIS public record for verification. Cross-reference the contaminant code on EPA's federal report to see violation dates, return-to-compliance status, and enforcement actions.
| Year (latest) | Contaminant | Category | Count | EPA Record |
|---|---|---|---|---|
| 2018 | Lead and Copper Rule | MR | 6 | SDWIS / CA5010039 / 5000 |
| 2017 | TTHM | MCL | 46 | SDWIS / CA5010039 / 2950 |
| 2009 | Consumer Confidence Rule | Other | 3 | SDWIS / CA5010039 / 7000 |
| 2009 | CARBON, TOTAL | MR | 2 | SDWIS / CA5010039 / 2920 |
| 2008 | Coliform (TCR) | MR | 7 | SDWIS / CA5010039 / 3100 |
| 2008 | Surface Water Treatment Rule | MR | 4 | SDWIS / CA5010039 / 0200 |
| 2006 | Total Haloacetic Acids (HAA5) | MCL | 14 | SDWIS / CA5010039 / 2456 |
| 2006 | Surface Water Treatment Rule | TT | 2 | SDWIS / CA5010039 / 0200 |
How WESTERN HILLS WATER DISTRICT/DIABLO GRAN Compares
Cross-reference this system's record against state averages and the federal MCL framework for context.
| Metric | WESTERN HILLS WATER DISTRICT/DIABLO GRAN | California avg | Federal benchmark |
|---|---|---|---|
| Total violations | 87 | 21.1 | SDWA compliance — any non-zero count is a recorded breach |
| Health-based violations | 62 | 8.8 | Indicates a contaminant exceeded a federal MCL |
| PFAS detection | None | 64.4% | EPA final rule (2024): PFOA/PFOS MCL = 4.0 ppt |
| Population served | 2,000 | 5,850 | Sizing context for compliance burden |
Sources: EPA SDWIS and EPA National Primary Drinking Water Regulations (40 CFR Part 141). State averages computed across 7,249 regulated public water systems in California.
Federal MCL reference — Safe Drinking Water Act thresholds ▼
| Contaminant | Federal MCL / Action Level | Note |
|---|---|---|
| Lead | 0 mg/L (Action Level: 0.015 mg/L) | Lead and Copper Rule treatment technique |
| Arsenic | 0.010 mg/L (10 ppb) | Health-based MCL since 2006 |
| Total Coliform | Treatment technique (RTCR) | Indicator organism, monitoring trigger |
| PFOA / PFOS (PFAS) | 4.0 ppt each (final 2024 rule) | Compliance deadline 2029 |
| Nitrate (as N) | 10 mg/L | Acute health risk for infants |
Frequently Asked Questions
Is WESTERN HILLS WATER DISTRICT/DIABLO GRAN water safe to drink? ▼
How many people does WESTERN HILLS WATER DISTRICT/DIABLO GRAN serve? ▼
What type of violations does WESTERN HILLS WATER DISTRICT/DIABLO GRAN have? ▼
Has PFAS been detected in WESTERN HILLS WATER DISTRICT/DIABLO GRAN water? ▼
What water source does WESTERN HILLS WATER DISTRICT/DIABLO GRAN use? ▼
Where does this data come from? ▼
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Related Data for California
Read our methodology — how this data is sourced, computed, and verified.