Community Water System · PWS CA5010039
Western Hills Water District/Diablo Gran
Operator location Patterson, California - 71% of 87 violations are health-based (upper-third health share (> 23%)); surface water source; 2,000 served per SDWIS.
- 2,000
- People served (this PWS)
- 87
- EPA violations (this PWS)
- 62
- Health-based (this PWS)
- Untested
- UCMR5 (this PWS)
Western Hills Water District/Diablo Gran standing, high SDWIS violation third
71% of 87 recorded violations are health-based - upper-third health share (> 23%). Corpus terciles use 29,740 systems serving 500+ (the sitemap cohort). Health-based share 71% is upper-third health share (> 23%). Population rank #13,545 of 29,740 among systems serving 500+.
The verdict
Western Hills Water District/Diablo Gran sits in the upper third of the sitemap cohort by violation count (87), so the tables below sample a dense compliance trail rather than a near-clean ledger. Population served is mid-pack at 2,000 (mid served population (≤ 3,309)). Health-based share is 71% - most of this ledger is MCL or treatment-technique exceedance. No UCMR5 PFAS test appears for this system in this extract.
- #13,545 of 29,740
- Population · /systems
- #910 of 1,701
- Population · CA
- 87
- Total EPA violations on record
- 71%
- Health-based (MCL / treatment failure)
Population ordinals match the sitemap cohort (systems serving 500+, population_served DESC). See methodology · corpus placement.
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 |
Violation Count vs. the National Corpus
Western Hills Water District/Diablo Gran has 87 recorded EPA violations, 70% of the 29,740 public water systems serving 500+ people nationwide carry fewer, and 30% carry more. 71% of this system's own violations are health-based (62 of 87), and it ranks #13,545 of 29,740 by population served among that same cohort.
EPA violations vs. the national water-system corpus
Public water systems serving 500+ people (EPA SDWIS)
87 Around the middle fewer violations than 30% of 29,740 water systems
the national water-system corpus, bucketed by value
Each bar is a band; taller bars hold more water systems. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA SDWIS · 2026-05-15
Health-based violations on Western Hills Water District/Diablo Gran
62 health-based rows in the tables above map to MCL or treatment-technique exceedances, verify each contaminant code on the federal SDWIS report for CA5010039.
Sources: EPA SDWIS · California State Water Resources Control Board, Division of Drinking Water
Nationwide peers
87 violations · 2,000 served: nearest cross-state SDWIS matches.
Cross-state systems with comparable violation load
Nearest cross-state community systems (500+ served) by total SDWIS violations on record.
Cross-state systems near this population served
Nearest cross-state systems by EPA SDWIS population_served (same 500+ sitemap gate).
What to do with Western Hills Water District/Diablo Gran
Use this system's EPA-reported record as a starting filter, not a final verdict.
- See how every tracked system in California compares on the same EPA violation measures. California systems
- Check whether PFAS was detected at this system under UCMR5 testing. PFAS guide
- Find and compare another public water system by name or PWSID. Search systems
EPA SDWIS and UCMR5 figures are informational only, not a substitute for a certified lab test of your own tap water.