Sonoma County Water Quality: 88 Violations (CA)
81 water systems · 63 ZIP codes · Grade B · Updated 2026-06-04
Data: EPA Safe Drinking Water Information System (SDWIS), EPA ECHO Last verified: 2026-06-04
Violation Trend
EPA violations across water systems in Sonoma County.
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Find the Right Filter →Water Quality Overview
Sonoma County has 81 community water systems serving approximately 17,265,838 people across 63 ZIP codes. These systems have accumulated 88 EPA violations, including 47 health-based violations.
Health-based violations account for 53% of all violations in Sonoma County. These violations indicate contaminant levels that may pose direct risks to human health.
Violation Breakdown
| Violation Type | Count | Percentage |
|---|---|---|
| Health-based | 47 | 53.4% |
| Monitoring/Reporting | 41 | 46.6% |
| Total | 88 | 100% |
Health-based violations indicate contaminant levels exceeding EPA Maximum Contaminant Levels (MCLs). Monitoring violations indicate failures to test or report.
Cities with Most Violations
| Rank | City | Violations | Health-Based | ZIP Codes | Population |
|---|---|---|---|---|---|
| 1 | Valley Ford | 25 | 24 | 1 | 1,157 |
| 2 | Moraga | 18 | 14 | 1 | 1,442,985 |
| 3 | Petaluma | 12 | 6 | 6 | 529,540 |
| 4 | Santa Rosa | 8 | 0 | 8 | 1,591,191 |
| 5 | Sebastopol | 4 | 2 | 2 | 216,474 |
| 6 | Sonoma | 4 | 1 | 1 | 182,197 |
| 7 | Forestville | 4 | 0 | 1 | 41,579 |
| 8 | Duncans Mills | 3 | 0 | 1 | 3,082 |
| 9 | Healdsburg | 2 | 0 | 1 | 46,383 |
| 10 | Occidental | 2 | 0 | 1 | 12,191 |
Violation Trend
Year-by-year EPA violations across water systems in Sonoma County:
| Year | Total | Health-Based |
|---|---|---|
| 2021 | 3 | 3 |
| 2022 | 4 | 4 |
| 2023 | 11 | 11 |
| 2024 | 32 | 32 |
| 2025 | 4 | 4 |
Most Common Contaminants
| Contaminant | Category | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|
| Stage 2 DBP Rule | Treatment Technique | 27 | 13 | Yes |
| Lead | Inorganic | 16 | 2 | Yes |
| Barium | Inorganic | 13 | 2 | Yes |
| Stage 1 DBP Rule | Treatment Technique | 12 | 12 | No |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 5 | 1 | Yes |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 4 | 2 | Yes |
Understanding Water Quality Scores
Each ZIP code in Sonoma County receives a safety score from 0-100 based on EPA compliance data. Scores factor in the number and severity of violations, with health-based violations weighted more heavily than monitoring failures. Resolved violations (where the system returned to compliance) receive reduced weight in the scoring.
The county-level grade (B) represents the average across all 63 ZIP codes. Individual ZIP codes may vary significantly — a county with a B grade may contain both A-rated and D-rated areas.
Water Systems in Sonoma County
Sonoma County is served by 81 community water systems, averaging 1.3 systems per ZIP code. Each system is independently regulated and tested by the EPA. Larger systems serving more people typically have more extensive monitoring requirements.
Water systems in Sonoma County source water from a mix of surface water (rivers, reservoirs) and groundwater (wells, aquifers). Source type affects which contaminants are most likely to be detected.
How to Check Your Water in Sonoma County
Enter your ZIP code on ZipCheckup for detailed water system data including contaminant levels, violation history, and safety scores
Request your CCR — every water utility must provide an annual Consumer Confidence Report
Get a home test — certified kits ($20-$50) or professional lab tests ($150-$400) can detect contaminants not covered by routine testing
Consider filtration — NSF-certified filters can address specific contaminants found in your area
Check for lead — homes built before 1986 should test for lead regardless of utility compliance
EPA Enforcement
The EPA and state regulators have taken 144 enforcement actions against water systems in Sonoma County. Enforcement actions range from compliance assistance and administrative orders to formal penalties. Systems under enforcement are required to remediate violations and may face ongoing monitoring requirements.
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Enforcement: EPA ECHO
Updated daily.
Water Quality Map: Sonoma County, CA
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Water Quality by ZIP Code in Sonoma County
Water quality varies across Sonoma County's 63 ZIP codes. Check your specific ZIP for detailed contaminant data.
| ZIP Code | City | Grade | Score | Violations | Health | |
|---|---|---|---|---|---|---|
| 94972 | Valley Ford | C | 60 | 25 | 24 | View → |
| 94556 | Moraga | C | 66 | 18 | 14 | View → |
| 95476 | Sonoma | B | 73 | 4 | 1 | View → |
| 95436 | Forestville | C | 64 | 4 | 0 | View → |
| 95430 | Duncans Mills | B | 84 | 3 | 0 | View → |
| 94955 | Petaluma | A | 94 | 2 | 1 | View → |
| 94975 | Petaluma | A | 94 | 2 | 1 | View → |
| 94999 | Petaluma | A | 94 | 2 | 1 | View → |
| 95473 | Sebastopol | A | 94 | 2 | 1 | View → |
| 94953 | Petaluma | A | 91 | 2 | 1 | View → |
| 95465 | Occidental | A | 89 | 2 | 0 | View → |
| 94954 | Petaluma | A | 86 | 2 | 1 | View → |
| 95448 | Healdsburg | B | 84 | 2 | 0 | View → |
| 95472 | Sebastopol | B | 81 | 2 | 1 | View → |
| 94952 | Petaluma | B | 76 | 2 | 1 | View → |
| 95406 | Santa Rosa | A | 99 | 1 | 0 | View → |
| 95402 | Santa Rosa | A | 95 | 1 | 0 | View → |
| 95409 | Santa Rosa | A | 95 | 1 | 0 | View → |
| 95403 | Santa Rosa | A | 90 | 1 | 0 | View → |
| 95404 | Santa Rosa | A | 90 | 1 | 0 | View → |
What are EPA health violations?
Health-based violations mean a contaminant was detected above the EPA's Maximum Contaminant Level (MCL) — the legal limit designed to protect human health. Sonoma County has 47 such violations. Not all violations cause illness, but repeated exceedances increase risk, especially for children and immunocompromised individuals.
What is a water quality grade?
ZipCheckup grades water systems from A to F based on EPA violation history, contaminant levels, and system compliance. Grade A means few or no violations; Grade F indicates persistent or serious issues. Sonoma County's overall grade is B.
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Find the Right Filter →Frequently Asked Questions
Is the tap water safe in Sonoma County, California?
Sonoma County has 81 community water systems with 88 recorded EPA violations, including 47 health-based. Water quality varies by ZIP code — check your specific location for detailed results.
How many water violations does Sonoma County have?
Sonoma County has 88 total EPA violations across 63 ZIP codes. 47 are health-based violations indicating contaminant levels potentially harmful to health.
Which city in Sonoma County has the most water violations?
Valley Ford has the most violations in Sonoma County with 25 recorded EPA violations across 1 ZIP codes.
What contaminants are found in Sonoma County water?
Sonoma County water systems are monitored for over 90 EPA-regulated contaminants including lead, copper, nitrates, disinfection byproducts, and bacteria. Check your ZIP code for contaminant-specific data.
How can I test my water in Sonoma County?
Contact your local water utility for free or low-cost testing. You can also use a certified home test kit ($20-$50) or hire a certified lab ($150-$400).