Diablo Grande, CA Tap Water Quality 2026

Water quality report for Diablo Grande, CA — PFAS, lead and copper results, violation history and state inspection findings from EPA SDWIS.

A look at Diablo Grande's drinking water using EPA enforcement records: violations, lead and copper results, PFAS sampling and state inspection findings.

Main Utility: Western Hills Water District/diablo Gran PWSID: CA5010039 Updated: 2026 Q2

✅

No federal limits exceeded on record

Lead was not detected and no violations are open. PFAS has never been sampled at this system.

Diablo Grande earns a B for water quality

Graded on violations and lead, with state inspection findings. PFAS not tested.

Lead: not detected

PFAS never sampled at this system

8 violations since 2015, 5 health-based

No violations currently open

Diablo Grande's lead level vs. all California community water systems

0 ppb5 ppb10 ppb15 ppb

Lead level: Not detected — 0% of the federal action level

✓ Lower lead than % of California utilities

Population Served

1669

~596 connections

Water Source

Surface water

Drawn from surface water — SDWIS source code SW

Active Violations

8 since 2015, all resolved

Lead & Copper Testing

Lead (Pb)

90th percentile of tap samples collected across the distribution system

0% of EPA action level

Not detected

Action level: 15 ppb

Lead was not detected at the 90th percentile — the result fell below the laboratory detection limit. That is not the same as an absence of lead in every tap, and older homes with lead service lines can still show higher readings.

Contaminant Violations (2015–Present)

Contaminant	Type	Measured	Limit	Period	Status
Lead and Copper Rule	MONITORING AND REPORTING	—	TT	2018	Resolved
TTHM	MCL EXCEEDANCE	0.086 MG/L	0.080 mg/L	2017	Resolved
TTHM	MCL EXCEEDANCE	0.109 MG/L	0.080 mg/L	2016	Resolved
Lead and Copper Rule	MONITORING AND REPORTING	—	TT	2016	Resolved
TTHM	MCL EXCEEDANCE	0.122 MG/L	0.080 mg/L	2016	Resolved
TTHM	MCL EXCEEDANCE	0.135 MG/L	0.080 mg/L	2016	Resolved
Lead and Copper Rule	MONITORING AND REPORTING	—	TT	2015	Resolved
TTHM	MCL EXCEEDANCE	0.115 MG/L	0.080 mg/L	2015	Resolved

Understanding violation types MCL violations mean a contaminant exceeded the federal maximum limit — the most serious type.
TT (Treatment Technique) violations mean required treatment procedures weren't followed, but don't necessarily mean contamination occurred.

Violation History

8 violations are on record since 2015, of which 5 were health-based. All have been resolved and none remain open.

About the Main Water System

Utility Western Hills Water District/Diablo Gran

PWSID CA5010039

Water source Surface water — Drawn from surface water — SDWIS source code SW

Population served 1,669

Service connections 596

Systems serving this area 1

Regulator State primacy agency

Data through 2026 Q2 — EPA SDWIS

Frequently Asked Questions

Is Diablo Grande tap water safe to drink? ▼

No federal limit is exceeded on record. No violations are currently open.

Does Diablo Grande water have PFAS? ▼

This system has never been sampled for PFAS. EPA's national monitoring covered systems serving 3,300 people or more, so no results exist — which is not evidence that none is present.

Who supplies water to Diablo Grande? ▼

Western Hills Water District/Diablo Gran (PWSID CA5010039). Surface water. Drawn from surface water — SDWIS source code SW

When was this system last inspected? ▼

It was last inspected on 2025-04-16. No significant deficiencies were recorded.

What Should Diablo Grande Residents Do?

Read your annual water report

Your supplier publishes a Consumer Confidence Report each July covering the prior year.

Check for a lead service line

Lead reaches tap water mainly through service lines and household plumbing. Suppliers now publish an inventory identifying lead lines.

Flush before drinking

If water has sat in pipes more than six hours, run the cold tap for two minutes before drinking or cooking.

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