WESTERN HILLS WATER DISTRICT/DIABLO GRAN
PWS ID: CA5010039 · PATTERSON, California 95363
Population Served
2,000
Total Violations
87
Health-Based Violations
62
Water Source
Surface Water
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 |
Data Sources: EPA Safe Drinking Water Information System (SDWIS), Q4 2025.
This data is provided for informational purposes only.