San Mateo County tap water
0 of 16 water systems serving San Mateo County with full PFAS testing averaged above a 2024 federal PFAS level at one or more sampling points.
- 36 community water systems list this county as served; 15 serve 3,300+ people with full PFAS testing.
- 4 had a health-based violation since 2021-10-26.
Largest systems serving this county
| System | Source | People served (whole system) | PFAS above a 2024 level? | Violations since 2021-10-26 |
|---|---|---|---|---|
| California Water Service - San Mateo | Purchased surface water | 103,536 | No | 0 |
| City of Daly City | Purchased surface water | 102,593 | No | 0 |
| California Water Service-S San Francisco | Purchased surface water | 62,609 | No | 0 |
| California Water Service - Bear Gulch | Surface water | 60,382 | No | 0 |
| City of San Bruno | Purchased surface water | 42,631 | No | 0 |
| North Coast County Water Dist | Purchased surface water | 38,546 | No | 0 |
| Estero Municipal Improvement District | Purchased surface water | 36,556 | No | 0 |
| California Water Service - San Carlos | Purchased surface water | 34,801 | No | 0 |
| Mid-Peninsula Water District | Purchased surface water | 31,059 | No | 0 |
| City of Millbrae | Purchased surface water | 22,795 | No | 0 |
| Menlo Park Municipal Water | Purchased surface water | 22,362 | No | 0 |
| Coastside County Water District | Surface water | 19,033 | No | 0 |
Which one is yours? A county usually has several utilities. Your bill or your utility's annual water-quality report names yours. Population is for the whole system, which can cross county lines.
Not medical or legal advice. UCMR 5 results are screening data, not compliance determinations.
Sources and freshness
Public-water-system facts, violations and lead/copper results: EPA ECHO SDWA download (SDWIS snapshot 2026-10-13). PFAS and lithium results: EPA UCMR 5 final data (sampling 2023–2025). Both are U.S. government works, downloaded 2026-10-26. Numbers are computed by the published method; the same fields are in the open data files.