Tuolumne County, California
16 ZIP codes · Avg score 64/100 · Grade C · Updated 2026-06-04
While Tuolumne County avoids the worst tiers, a portion of its 16 ZIP codes have logged violations.
How Tuolumne County Compares
How Tuolumne County Compares
Tuolumne County scores 9 points below the California state average (73/100) and 4 points below the national average (68/100).
Data: EPA SDWIS Last verified: 2026-06-04
ZIP Code Risk Map
Water Quality Map: Tuolumne County, California
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Key Risk Factors
Health risk index: 13.2 (asthma 10.3%, diabetes 12.2%)
Estimated additional annual cost per homeowner: $2,078, driven primarily by wildfire
Infrastructure: 0.377% avg pipe failure probability, 29% of ZIPs at high risk
70.3% of homes built before 1978 (lead paint era)
Violation History (2021–2025)
→ Stable trendEPA violation counts by year across Tuolumne County water systems. Health-based shown in red, total in blue.
Peak year: 2024 with 16 violations. Past 5 years: 25 total (25 health-based).
Source: EPA SDWIS historical violations. Data may lag 6–12 months for the most recent year.
County Health Indicators vs National Average
Black markers indicate national averages. Source: CDC PLACES, Census ACS.
Infrastructure Overview
Sources: Census ACS (housing age), EPA SDWIS (infrastructure risk model), state bridge inspection data.
Compound Risk Breakdown
Estimated additional annual cost per homeowner: $2,078
Bar widths proportional to share of total annual risk cost. Source: compound risk model (FEMA, EPA, USGS).
Housing Age Distribution
31,931 housing units in Tuolumne County
Source: U.S. Census Bureau ACS B25034 (Year Structure Built).
Water Safety Affordability
How much it costs to fix water issues relative to home values in Tuolumne County
Remediation costs are relatively manageable for most homeowners in Tuolumne County, representing a small fraction of property value.
Remediation includes water filtration, lead abatement, radon mitigation, and flood protection where applicable. Source: Census ACS, EPA SDWIS.
Health Outcomes vs National Average
CDC PLACES data for Tuolumne County residents
Black markers = national averages. Red = above national avg. Green = below. Source: CDC PLACES, Census ACS.
Water Systems with Most Violations
Top 5 systems in Tuolumne County ranked by EPA violation count.
| # | Water System | Population | Violations |
|---|---|---|---|
| 1 | Tud - Ponderosa | 1,767 | 11 |
| 2 | Bluebell Valley Mwc | 282 | 10 |
| 3 | Tud - Columbia Water System | 5,463 | 9 |
| 4 | Tud - Upper Basin Water System | 13,280 | 9 |
| 5 | Twain Harte Community Services District | 2,378 | 9 |
27 total water systems serve Tuolumne County.
All ZIP Codes in Tuolumne County
16 ZIP codes tracked in Tuolumne County.
| # | ZIP Code | City | Safety Score | Grade | Violations | Home Value |
|---|---|---|---|---|---|---|
| 1 | 95310 | Columbia | 83 | B | 1 | $449K |
| 2 | 95379 | Tuolumne | 83 | B | 1 | $405K |
| 3 | 95327 | Jamestown | 75 | B | 7 (5 health) | $367K |
| 4 | 95372 | Soulsbyville | 71 | B | 5 (1 health) | $354K |
| 5 | 95373 | Standard | 71 | B | 2 | — |
| 6 | 95335 | Long Barn | 70 | B | 2 | $248K |
| 7 | 95370 | Sonora | 70 | B | 1 | $416K |
| 8 | 95321 | Groveland | 67 | C | 6 (3 health) | $377K |
| 9 | 95383 | Twain Harte | 60 | C | 4 (1 health) | $454K |
| 10 | 95346 | Mi Wuk Village | 55 | C | 4 (1 health) | $516K |
| 11 | 95364 | Pinecrest | 55 | C | 3 (1 health) | — |
| 12 | 95305 | Big Oak Flat | 53 | D | 0 | — |
| 13 | 95309 | Chinese Camp | 53 | D | 0 | — |
| 14 | 95311 | Coulterville | 53 | D | 0 | $296K |
| 15 | 95347 | Moccasin | 53 | D | 0 | — |
| 16 | 95375 | Strawberry | 53 | D | 0 | — |
Recommended Buyer Guides for Tuolumne County
Eight risk categories drive the selection — PFAS exceedance, lead above EPA action level, pre-1978 housing share, EPA Radon Zone 1, flood-top-risk, wildfire-top-risk, multi-contaminant load, and a baseline fallback — and each category maps to a specific buyer-guide track that surfaces when the county data hits its threshold for that hazard signal.
- Best Lead Paint Test Kits — 70.3% of homes built before 1978
- Best Under-Sink Reverse Osmosis Systems — Multi-contaminant removal at the kitchen tap
- Best HEPA Air Purifiers for Wildfire Smoke — Wildfire is the top compound risk factor
Deep Dive Reports
Detailed analysis for Tuolumne County, California
Overview
Tuolumne County in California covers 16 ZIP codes with an average Home Safety Score of C (64/100).
11 of 16 ZIP codes have recorded EPA violations. 12 health-based violations have been documented.
← Back to California water quality report
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Home values: U.S. Census Bureau ACS (median estimates by ZCTA)
Updated daily.