County · California
San Mateo County, California: drinking water records
This overview covers 30 ZIP codes and 36 community water systems in San Mateo County. It also stands in for 1 ZIP codes whose utility has too little EPA data for a page of its own.
System population figures are summed from EPA registry records and can overlap where wholesalers and retail systems serve the same people. They are not a Census county-population estimate.
Water systems with the most complete records
| Water system | People served | PFAS survey results | PFAS found | Health-based violations | Lead, 9 in 10 homes at or below |
|---|---|---|---|---|---|
| City of Daly City CA4110013 | 104,901 | 525 | 0 | 0 | 0 ppb |
| California Water Service - San Mateo CA4110008 | 102,348 | 120 | 0 | 0 | 4.4 ppb |
| City of Redwood City CA4110022 | 92,819 | 95 | 0 | 0 | 0 ppb |
| California Water Service-S San Francisco CA4110009 | 64,146 | 180 | 0 | 0 | 4.1 ppb |
| California Water Service - Bear Gulch CA4110006 | 61,431 | 120 | 0 | 0 | 4 ppb |
| City of San Bruno CA4110023 | 42,631 | 360 | 0 | 0 | 0 ppb |
| North Coast County Water Dist CA4110025 | 38,546 | 120 | 0 | 0 | 0 ppb |
| Estero Municipal Improvement District CA4110021 | 36,556 | 120 | 0 | 0 | 0 ppb |
| California Water Service - San Carlos CA4110007 | 35,344 | 120 | 0 | 0 | 5.8 ppb |
| City of Burlingame CA4110003 | 31,451 | 90 | 0 | 0 | 6.3 ppb |
| Mid-Peninsula Water District CA4110001 | 30,609 | 120 | 0 | 0 | 0 ppb |
| City of East Palo Alto CA4110024 | 29,519 | 90 | 0 | 0 | 0 ppb |
| City of Millbrae CA4110018 | 22,795 | 120 | 0 | 0 | 0 ppb |
| Menlo Park Municipal Water CA4110017 | 22,362 | 120 | 0 | 0 | 3.1 ppb |
| Coastside County Water District CA4110011 | 18,940 | 240 | 0 | 0 | 1.6 ppb |
| Westborough Water District CA4110027 | 13,486 | 120 | 0 | 0 | 0 ppb |
| Town of Hillsborough CA4110016 | 11,766 | 120 | 0 | 0 | 0 ppb |
| Montara Water and Sanitary District CA4110010 | 6,078 | 240 | 0 | 0 | 0 ppb |
| O'Connor Tract Co-Operative Water Co. CA4110019 | 2,789 | 0 | 0 | 1 | 0 ppb |
| Guadalupe Valley Mid CA4110005 | 1,472 | 120 | 6 | 0 | 0 ppb |
| Cuesta la Honda Guild INC CA4110012 | 915 | 0 | 0 | 4 | 0 ppb |
| County Service Area 11 CA4100582 | 642 | 0 | 0 | 1 | 0.6 ppb |
| County Service Area 7 CA4100509 | 300 | 0 | 0 | 6 | 2.1 ppb |
| Camp Loma Mar CA4100529 | 208 | 0 | 0 | 1 | 0 ppb |
| Redwood Terrace Mutual CA4100510 | 56 | 0 | 0 | 1 | 7 ppb |
ZIP reports in San Mateo County
No ZIP report in this county is published yet.
These ZIP codes are covered by this overview because their utility has too little EPA data for a separate page: 94128.
Sources and scope
EPA UCMR 5 occurrence data, samples collected 2023-01-03 – 2026-06-17, final release, August 2026 (file dated Aug 28, 2026); EPA SDWIS via ECHO, 2026Q2 extract (file dated Jul 9, 2026); EPA service-area boundaries v3.0; Census 2020 ZCTAs. Page generated 2026-09-03.
Counts cover the systems that report this county to EPA. A water system may cross county lines. "Found" means at least one result at or above the laboratory reporting level; it is not a compliance finding.