Mariposa County, California
6 ZIP codes · Avg score 58/100 · Grade C · Updated 2026-06-04
Across Mariposa County, EPA compliance data for 6 ZIP codes sits at a moderate level — not alarming, but not uniformly clean either.
How Mariposa County Compares
How Mariposa County Compares
Mariposa County scores 15 points below the California state average (73/100) and 10 points below the national average (68/100).
Data: EPA SDWIS Last verified: 2026-06-04
ZIP Code Risk Map
Water Quality Map: Mariposa County, California
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Key Risk Factors
Health risk index: 14 (asthma 10.3%, diabetes 13.5%)
Estimated additional annual cost per homeowner: $1,973, driven primarily by wildfire
Infrastructure: 0.39% avg pipe failure probability, 17% of ZIPs at high risk
71.5% of homes built before 1978 (lead paint era)
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: $1,973
Bar widths proportional to share of total annual risk cost. Source: compound risk model (FEMA, EPA, USGS).
Housing Age Distribution
7,419 housing units in Mariposa 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 Mariposa County
Remediation costs are relatively manageable for most homeowners in Mariposa 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 Mariposa 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 Mariposa County ranked by EPA violation count.
| # | Water System | Population | Violations |
|---|---|---|---|
| 1 | MARIPOSA PUBLIC UTILITY DIST | 2,000 | 1 |
| 2 | Ponderosa Basin Mutual Wtr Company | 798 | 1 |
| 3 | Yosemite West Water System | 420 | 1 |
| 4 | Mariposa Pines Mutual | 284 | 1 |
| 5 | Mpwd-coulterville Csa 1 | 193 | 1 |
6 total water systems serve Mariposa County.
All ZIP Codes in Mariposa County
6 ZIP codes tracked in Mariposa County.
| # | ZIP Code | City | Safety Score | Grade | Violations | Home Value |
|---|---|---|---|---|---|---|
| 1 | 95338 | Mariposa | 81 | B | 1 | $367K |
| 2 | 95306 | Catheys Valley | 53 | D | 0 | — |
| 3 | 95318 | El Portal | 53 | D | 0 | $298K |
| 4 | 95325 | Hornitos | 53 | D | 0 | — |
| 5 | 95345 | Midpines | 53 | D | 0 | $416K |
| 6 | 95389 | Yosemite National Park | 53 | D | 0 | $913K |
Recommended Buyer Guides for Mariposa County
Independent picks. EPA-grounded. Matched here.
- Best Lead Paint Test Kits — 71.5% of homes built before 1978
- Best HEPA Air Purifiers for Wildfire Smoke — Wildfire is the top compound risk factor
Deep Dive Reports
Detailed analysis for Mariposa County, California
Overview
Mariposa County in California covers 6 ZIP codes with an average Home Safety Score of C (58/100).
1 of 6 ZIP codes have recorded EPA violations. All violations are monitoring/reporting type.
← 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.