San Mateo County, California
35 ZIP codes · Avg score 72/100 · Grade B · Updated 2026-06-03
For households in San Mateo County, the 35 ZIP codes on record show consistently safe tap water.
How San Mateo County Compares
How San Mateo County Compares
San Mateo County scores 1 points below the California state average (73/100) and 4 points above the national average (68/100).
Data: EPA SDWIS Last verified: 2026-06-03
ZIP Code Risk Map
Water Quality Map: San Mateo County, California
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Key Risk Factors
Health risk index: 9.6 (asthma 8.5%, diabetes 10.6%)
Estimated additional annual cost per homeowner: $3,873, driven primarily by sea_level
Infrastructure: 0.388% avg pipe failure probability, 35% of ZIPs at high risk
78.7% of homes built before 1978 (lead paint era)
Violation History (2021–2025)
↑ Worsening trendEPA violation counts by year across San Mateo County water systems. Health-based shown in red, total in blue.
Peak year: 2024 with 14 violations. Past 5 years: 32 total (32 health-based). Health-based violations are rising versus the prior 2-year window — worth closer monitoring.
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: $3,873
Bar widths proportional to share of total annual risk cost. Source: compound risk model (FEMA, EPA, USGS).
Housing Age Distribution
272,868 housing units in San Mateo 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 San Mateo County
Remediation costs are relatively manageable for most homeowners in San Mateo 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 San Mateo 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 San Mateo County ranked by EPA violation count.
| # | Water System | Population | Violations |
|---|---|---|---|
| 1 | Lazy B Mobilehome Park | 125 | 20 |
| 2 | Blue Lakes Mobile Home Park | 32 | 20 |
| 3 | Butano Canyon Mutual | 150 | 9 |
| 4 | Bianchi Flowers Inc. | 65 | 9 |
| 5 | Marchi Central Farm | 50 | 9 |
41 total water systems serve San Mateo County.
All ZIP Codes in San Mateo County
35 ZIP codes tracked in San Mateo County.
| # | ZIP Code | City | Safety Score | Grade | Violations | Home Value |
|---|---|---|---|---|---|---|
| 1 | 94005 | Brisbane | 83 | B | 0 | $1127K |
| 2 | 94021 | Loma Mar | 83 | B | 0 | $1021K |
| 3 | 94026 | Menlo Park | 83 | B | 0 | — |
| 4 | 94083 | South San Francisco | 83 | B | 0 | — |
| 5 | 94064 | Redwood City | 82 | B | 1 (1 health) | — |
| 6 | 94065 | Redwood City | 82 | B | 1 (1 health) | $1847K |
| 7 | 94002 | Belmont | 78 | B | 0 | $2000K |
| 8 | 94019 | Half Moon Bay | 78 | B | 0 | $1509K |
| 9 | 94066 | San Bruno | 78 | B | 0 | $1199K |
| 10 | 94061 | Redwood City | 77 | B | 1 (1 health) | $1938K |
| 11 | 94062 | Redwood City | 77 | B | 1 (1 health) | $2000K |
| 12 | 94016 | Daly City | 76 | B | 0 | — |
| 13 | 94017 | Daly City | 76 | B | 0 | — |
| 14 | 94037 | Montara | 75 | B | 0 | $1467K |
| 15 | 94011 | Burlingame | 74 | B | 0 | — |
| 16 | 94020 | La Honda | 74 | B | 5 (4 health) | $1158K |
| 17 | 94014 | Daly City | 73 | B | 0 | $980K |
| 18 | 94015 | Daly City | 73 | B | 0 | $1153K |
| 19 | 94025 | Menlo Park | 73 | B | 0 | $2000K |
| 20 | 94044 | Pacifica | 73 | B | 0 | $1212K |
| 21 | 94080 | South San Francisco | 73 | B | 0 | $1160K |
| 22 | 94063 | Redwood City | 72 | B | 1 (1 health) | $1077K |
| 23 | 94030 | Millbrae | 68 | C | 2 (1 health) | $1930K |
| 24 | 94497 | San Mateo | 68 | C | 4 (3 health) | — |
| 25 | 94010 | Burlingame | 67 | C | 0 | $2000K |
| 26 | 94401 | San Mateo | 66 | C | 4 (3 health) | $1123K |
| 27 | 94402 | San Mateo | 66 | C | 4 (3 health) | $2000K |
| 28 | 94403 | San Mateo | 66 | C | 4 (3 health) | $1726K |
| 29 | 94404 | San Mateo | 66 | C | 4 (3 health) | $1683K |
| 30 | 94018 | El Granada | 63 | C | 0 | $1405K |
| 31 | 94038 | Moss Beach | 63 | C | 0 | $1113K |
| 32 | 94060 | Pescadero | 63 | C | 9 (1 health) | $1338K |
| 33 | 94028 | Portola Valley | 55 | C | 0 | $2000K |
| 34 | 94128 | San Francisco | 53 | D | 7 (6 health) | — |
| 35 | 94070 | San Carlos | 50 | D | 0 | $2000K |
Recommended Buyer Guides for San Mateo County
Strictly editorial — no paid placements influence which guides appear; the selection draws on NSF certifications and EPA detection records for water systems serving this county.
- Best Lead Paint Test Kits — 78.7% of homes built before 1978
- Best Under-Sink Reverse Osmosis Systems — Multi-contaminant removal at the kitchen tap
Deep Dive Reports
Detailed analysis for San Mateo County, California
Overview
San Mateo County in California covers 35 ZIP codes with an average Home Safety Score of B (72/100).
14 of 35 ZIP codes have recorded EPA violations. 32 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.