Tuolumne County Water Quality: 64 Violations (CA)
14 water systems · 9 ZIP codes · Home Safety Score 75/100 (B) · 7 of 15 tracked ZIP records scored · Updated
Data: EPA Safe Drinking Water Information System (SDWIS), EPA ECHO Last verified:
Violation Trend
EPA violations across water systems in Tuolumne County.
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Find the Right Filter →Water Quality Overview
Tuolumne County has 14 community water systems across 9 directly mapped ZIP records. The systems report serving approximately 47,257 people. The available records contain 64 EPA violations, including 13 health-based violations.
Health-based violations account for 20% of all violations in Tuolumne County. These violations indicate contaminant levels that may pose direct risks to human health.
Violation Breakdown
| Violation Type | Count | Percentage |
|---|---|---|
| Health-based | 13 | 20.3% |
| Monitoring/Reporting | 51 | 79.7% |
| Total | 64 | 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 | Sonora | 13 | 1 | 1 | 28,373 |
| 2 | Twain Harte | 13 | 2 | 1 | 3,663 |
| 3 | Mi Wuk Village | 12 | 2 | 1 | 807 |
| 4 | Big Oak Flat | 10 | 4 | 1 | 203 |
| 5 | Jamestown | 8 | 1 | 1 | 8,799 |
| 6 | Groveland | 5 | 3 | 1 | 3,870 |
| 7 | Tuolumne | 1 | 0 | 1 | 3,821 |
| 8 | Soulsbyville | 1 | 0 | 1 | 1,825 |
| 9 | Columbia | 1 | 0 | 1 | 1,783 |
Violation Trend
Year-by-year EPA violations across water systems in Tuolumne County:
| Year | Total | Health-Based |
|---|---|---|
| 2021 | 3 | 3 |
| 2024 | 11 | 11 |
| 2025 | 4 | 4 |
Most Common Contaminants
| Contaminant | Category | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|
| Stage 2 DBP Rule | Treatment Technique | 20 | 6 | Yes |
| Lead | Inorganic | 9 | 6 | No |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 4 | 2 | Yes |
| Stage 1 DBP Rule | Treatment Technique | 2 | 2 | No |
Water Data and the Home Safety Score
This page reports EPA water-system facts without converting the broader Home Safety Score into a drinking-water grade. The county Home Safety grade (B) is a separate multi-source index that also requires PFAS screening, radon, and annual air-quality evidence. Check each ZIP report for the versioned score and its component coverage.
Water Systems in Tuolumne County
Tuolumne County is served by 14 community water systems, averaging 0.9 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 Tuolumne 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 Tuolumne County
Enter your ZIP code on ZipCheckup for detailed water-system data including contaminant levels and violation history; the Home Safety Score is shown separately with its model version
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 69 enforcement actions against water systems in Tuolumne 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
Source publication schedules vary. See the page source and verification fields for available timing evidence.
Water Quality by ZIP Code in Tuolumne County
Water quality varies across Tuolumne County's 9 ZIP codes. Check your specific ZIP for detailed contaminant data.
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. Tuolumne County has 13 such violations. Not all violations cause illness, but repeated exceedances increase risk, especially for children and immunocompromised individuals.
Water facts and the Home Safety Score
The score shown here is the broader Home Safety Score, not a water-quality grade. Model 4.0.0 combines EPA SDWIS identity plus accepted ECHO SDWA lifecycle-based water compliance, PFAS screening, radon zones, and annual air-quality evidence. Tuolumne County has a score of 75/100 (Grade B) across 7 scored of 15 tracked ZIP records.
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Find the Right Filter →Frequently Asked Questions
Is the tap water safe in Tuolumne County, California?
Tuolumne County has 14 community water systems with 64 recorded EPA violations, including 13 health-based. Water quality varies by ZIP code - check your specific location for detailed results.
How many water violations does Tuolumne County have?
Tuolumne County has 64 total EPA violations across 9 directly mapped ZIP records. 13 are health-based.
Which city in Tuolumne County has the most water violations?
Sonora has the most violations in Tuolumne County with 13 recorded EPA violations across 1 ZIP code.
What contaminants are found in Tuolumne County water?
Tuolumne 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 Tuolumne 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).