San Mateo, CA: 15 Health Violations — 66/100 (2026)
5 ZIP codes · 2 water systems · Updated 2026-06-03
Compliance figures for San Mateo indicate average water quality in CA overall — some service areas have recorded health-based violations in recent monitoring cycles, while others operate cleanly, making system-level data the most actionable reference point for residents.
How San Mateo Compares
Data: EPA SDWIS Last verified: 2026-06-03
Water Quality Map: San Mateo, CA
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Score Distribution
Safety grade breakdown for San Mateo's 5 ZIP codes.
Key Facts for San Mateo Residents
- Your city's water systems recorded 20 violations in the past 5 years.
- Average lead level: 0.0017 mg/L.
- Homes built before 1986: 79% — older plumbing may contain lead solder.
- Estimated remediation: $1,560 per household.
- CDC health risk index: 9.58.
San Mateo's Water Providers
Residential addresses in San Mateo, CA are served by 2 primary water providers out of 2 systems in federal records. Each system maintains separate infrastructure and files its own EPA compliance reports, so service conditions are not uniform across the city.
Overview
We track water quality and home safety data for 5 ZIP codes in San Mateo, California, covering 2 community water systems serving approximately 140,535 people.
5 of 5 ZIP codes (100%) have recorded EPA violations. 15 health-based violations documented.
Home Safety Score
Average Home Safety Score for San Mateo: C (66/100)
The score combines three factors:
| Factor | What It Measures |
|---|---|
| Water Quality | EPA violations and compliance history |
| Lead Levels | 90th percentile lead concentration vs EPA action level |
| Radon Risk | EPA radon zone classification |
Water Sources
San Mateo water systems draw from: Groundwater.
Lead & Copper
- Average lead level (90th percentile): 0.0017 mg/L (EPA action level: 0.015 mg/L)
- 0 ZIP codes exceed the EPA lead action level
Radon Risk
Dominant radon zone: Zone 2 (Moderate Risk)
- Zone 1 (High): 0 ZIP codes
- Zone 2 (Moderate): 5 ZIP codes
- Zone 3 (Low): 0 ZIP codes
The EPA recommends testing homes in Zone 1 and Zone 2 areas for radon.
Top Contaminants
| Contaminant | Category | Violations | ZIPs Affected |
|---|---|---|---|
| Lead | Inorganic | 12 | 5 |
| Stage 2 DBP Rule | Treatment Technique | 12 | 5 |
Areas with Most Violations
| ZIP Code | Safety Score | Violations | Health-Based | System |
|---|---|---|---|---|
| 94401 | C | 4 | 3 | Lazy B Mobilehome Park |
| 94402 | C | 4 | 3 | Lazy B Mobilehome Park |
| 94403 | C | 4 | 3 | Lazy B Mobilehome Park |
| 94404 | C | 4 | 3 | Lazy B Mobilehome Park |
| 94497 | C | 4 | 3 | Lazy B Mobilehome Park |
All ZIP Codes in San Mateo
- 94401 [C] — 4 violations ⚠
- 94402 [C] — 4 violations ⚠
- 94403 [C] — 4 violations ⚠
- 94404 [C] — 4 violations ⚠
- 94497 [C] — 4 violations ⚠
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Lead/copper: EPA Lead and Copper Rule sampling data
- Radon: EPA Map of Radon Zones
Updated daily.
San Mateo Community Health Snapshot
Source: CDC PLACES (County-level estimates). Water contamination can correlate with respiratory and chronic health conditions.
Compared to National Average
Vertical line = national average. ■ Above national · ■ Below national
What's in San Mateo's Water?
Based on EPA violation records. Check your ZIP code report for system-specific contaminant data.
San Mateo Infrastructure Age
With 79% of homes built before 1986, lead solder in plumbing is a potential concern. The EPA banned lead solder in 1986, but many older homes retain original plumbing.
Source: U.S. Census Bureau American Community Survey (ACS).
Housing Age Profile
Viewed through the lens of construction era, San Mateo is predominantly an older city — a median build year of 1964 puts most of the residential inventory in the range where pre-1986 plumbing materials were the standard.
Over half of homes in San Mateo were built before 1986, when lead solder was banned. Older plumbing may leach lead into drinking water, especially with corrosive water chemistry.
Source: U.S. Census Bureau ACS B25034.
How Remediation Costs Compare in San Mateo
Placing remediation in the context of San Mateo's property market, the equity share is low — most homeowners here are weighing a financial commitment that fits comfortably within routine property planning, far from the threshold where remediation becomes a material equity decision rather than a standard upkeep consideration.
Remediation costs in San Mateo are relatively low compared to home values. The $940–$2,940 estimated range is a small fraction of median property value. Home values are 134% above the California average.
San Mateo: Lead Risk & Vulnerable Populations
Why children are most at risk: The CDC states there is no safe level of lead exposure for children. Children under 6 absorb lead more readily than adults, and even low levels can cause developmental delays, learning difficulties, and behavioral problems.
Practically, the structural drivers in San Mateo — 79% pre-rule stock and citywide monitoring at or beyond the regulatory benchmark — make an in-home draw the practical way to translate aggregate averages into the specific conditions at one address.
Sources: EPA Lead and Copper Rule, U.S. Census Bureau ACS, CDC childhood lead poisoning prevention guidelines.
San Mateo: Flood History & Water Damage Risk
Flood activity in San Mateo is neither negligible nor at the level of the highest-exposure areas in the NFIP dataset. The 124-claim record and 80% flood zone coverage suggest a community that has experienced recurrent events but has not faced the kind of sustained, severe exposure where water-supply contamination becomes a primary public health concern. It sits in a middle range where flood history merits inclusion in any complete local water quality picture.
San Mateo has a moderate flood history with 124 FEMA claims averaging $9,677 per payout. 80% of ZIP codes fall within FEMA flood zones. Flood events can contaminate drinking water and overwhelm treatment systems.
How flooding affects water quality: Flood events can introduce sewage, agricultural runoff, and industrial chemicals into water supplies. Even after floodwaters recede, contamination can persist in wells and aging infrastructure. Flood damage can add significantly to the estimated <strong>$1,560</strong> remediation cost per household.
Residents in flood-prone areas should consider flood insurance even outside FEMA zones — over 25% of flood claims come from low-to-moderate risk areas. After any flood event, test your water before drinking.
Source: FEMA National Flood Insurance Program (NFIP) claims data, FEMA flood zone designations.
What You Can Do in San Mateo
- Test your water at home. City-level data shows averages — your tap may differ. NSF-certified test kits cost $20-40 and give results in days.
- Install a certified water filter. Filters rated for Lead can reduce the most common contaminant found in San Mateo's water.
- Check your home's plumbing. With 79% of homes built before 1986, lead solder is a real possibility.
Deep Dive Reports
Detailed analysis for San Mateo, CA