Lead in San Mateo, CA Drinking Water
Lead data for San Mateo, California · 140,535 residents · 5 ZIP codes
For residents of San Mateo, California, Lead has appeared in public water supply sampling data.
Data: EPA SDWIS, CCR Reports, ECHO Last verified: 2026-04-05
Lead in San Mateo Tap Water
Lead has been detected in San Mateo, California drinking water at a maximum level of 1.7 ppb — below the EPA action level of 15 ppb (action level).
This analysis covers 140,535 residents across 5 ZIP codes in San Mateo.
San Mateo's overall water quality grade is C (66/100).
Is Lead in San Mateo Water Safe?
If you live in an affected ZIP code, consider installing a reverse osmosis or nsf 53 carbon block filter certified under NSF 53 / NSF 58 and testing your water independently.
Lead Levels by ZIP Code
| ZIP Code | Lead Level | EPA Limit | Status |
|---|---|---|---|
| 94401 | 1.7 ppb | 15 ppb (action level) | OK |
| 94402 | 1.7 ppb | 15 ppb (action level) | OK |
| 94403 | 1.7 ppb | 15 ppb (action level) | OK |
| 94404 | 1.7 ppb | 15 ppb (action level) | OK |
| 94497 | 1.7 ppb | 15 ppb (action level) | OK |
Average lead level across San Mateo: 1.7 ppb
EPA Violations for Lead in San Mateo
| Date | Violation Type | Status | ZIP Code |
|---|---|---|---|
| 2024-01-01 | Lead (Known) | Known | 94401 |
| 2024-01-01 | Lead (Known) | Known | 94402 |
| 2024-01-01 | Lead (Known) | Known | 94403 |
| 2024-01-01 | Lead (Known) | Known | 94404 |
| 2024-01-01 | Lead (Known) | Known | 94497 |
| 2023-10-01 | Lead (Known) | Known | 94401 |
| 2023-10-01 | Lead (Known) | Known | 94402 |
| 2023-10-01 | Lead (Known) | Known | 94403 |
| 2023-10-01 | Lead (Known) | Known | 94404 |
| 2023-10-01 | Lead (Known) | Known | 94497 |
Health Effects of Lead
- Brain development delays and reduced IQ in children
- Behavioral problems and learning disabilities
- High blood pressure and kidney damage in adults
- Increased risk of premature birth in pregnant women
Health risk severity: High. Governed by the Lead and Copper Rule Revisions (LCRR/LCRI).
How Lead Gets Into Drinking Water
- Corrosion of lead service lines (pipes connecting water main to home)
- Lead solder in copper plumbing joints (pre-1986 homes)
- Brass fixtures and faucets manufactured before 2014
- Stagnant water that sits in lead-containing pipes overnight
What to Do About Lead in San Mateo Water
- Install an NSF 53 or NSF 58 certified filter at kitchen sink
- Run cold water for 30 seconds before using for drinking or cooking
- Use cold water only for cooking and preparing formula
- Consider whole-home reverse osmosis if lead service line is present
Look for filters certified under NSF 53 / NSF 58 for lead removal.