Napa County, California
13 ZIP codes · Avg score 71/100 · Grade B · Updated 2026-06-03
Napa County — 13 ZIP codes, above-average safety grade.
How Napa County Compares
How Napa County Compares
Napa County scores 2 points below the California state average (73/100) and 3 points above the national average (68/100).
Data: EPA SDWIS Last verified: 2026-06-03
ZIP Code Risk Map
Water Quality Map: Napa County, California
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Key Risk Factors
Health risk index: 11.6 (asthma 9.5%, diabetes 11.4%)
Estimated additional annual cost per homeowner: $2,589, driven primarily by flood
Infrastructure: 0.4% avg pipe failure probability, 50% of ZIPs at high risk
69.4% of homes built before 1978 (lead paint era)
Violation History (2021–2024)
↓ Improving trendEPA violation counts by year across Napa County water systems. Health-based shown in red, total in blue.
Peak year: 2022 with 14 violations. Past 5 years: 34 total (34 health-based). Health-based violations are declining versus the prior 2-year window.
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: $2,589
Bar widths proportional to share of total annual risk cost. Source: compound risk model (FEMA, EPA, USGS).
Housing Age Distribution
74,082 housing units in Napa 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 Napa County
Remediation costs are relatively manageable for most homeowners in Napa 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 Napa 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 Napa County ranked by EPA violation count.
| # | Water System | Population | Violations |
|---|---|---|---|
| 1 | Howell Mountain Mutual Water Company | 1,240 | 13 |
| 2 | City of Calistoga, | 5,610 | 9 |
| 3 | Windsor, Town of | 25,561 | 9 |
| 4 | Tucker Acres Mutual Water Company | 200 | 9 |
| 5 | City of Napa, | 84,804 | 6 |
24 total water systems serve Napa County.
All ZIP Codes in Napa County
13 ZIP codes tracked in Napa County.
| # | ZIP Code | City | Safety Score | Grade | Violations | Home Value |
|---|---|---|---|---|---|---|
| 1 | 94550 | Livermore | 95 | A | 0 | $1147K |
| 2 | 94503 | American Canyon | 87 | A | 0 | $664K |
| 3 | 94508 | Angwin | 86 | A | 4 (4 health) | $775K |
| 4 | 94599 | Yountville | 79 | B | 3 (1 health) | $757K |
| 5 | 94562 | Oakville | 73 | B | 0 | — |
| 6 | 94573 | Rutherford | 73 | B | 0 | — |
| 7 | 94515 | Calistoga | 70 | B | 9 (8 health) | $831K |
| 8 | 94567 | Pope Valley | 66 | C | 0 | $386K |
| 9 | 94576 | Deer Park | 66 | C | 0 | $1059K |
| 10 | 94581 | Napa | 64 | C | 1 | — |
| 11 | 94574 | Saint Helena | 60 | C | 0 | $1877K |
| 12 | 94558 | Napa | 53 | D | 1 | $856K |
| 13 | 94559 | Napa | 53 | D | 1 | $877K |
Recommended Buyer Guides for Napa County
Editorial-only picks, screened against the EPA detections on file.
- Best Water Filters for Lead — Lead above EPA action level in 3 ZIP codes
- Best Lead Paint Test Kits — 69.4% of homes built before 1978
- Best Under-Sink Reverse Osmosis Systems — Multi-contaminant removal at the kitchen tap
- Best Sump Pumps — Flood is the top compound risk factor
- Best Mold Test Kits — Flood-driven moisture and mold risk
Deep Dive Reports
Detailed analysis for Napa County, California
Overview
Napa County in California covers 13 ZIP codes with an average Home Safety Score of B (71/100).
6 of 13 ZIP codes have recorded EPA violations. 13 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.