PlainWater
Counties → California

San Mateo County, California

Water Systems
52
Population Served
782,067
Total Violations
1,318
243 health-based
PFAS Detected
4
of 19 tested

Violation Analysis

96.2%
Systems with Violations
25.3
Avg Violations per System
18.4%
Health-Based Violations

Water Source Types

SW
34 systems (65%)
GW
16 systems (31%)

PFAS Contamination

19
Systems Tested
4
PFAS Detected
21.1%
Detection Rate

PFAS (per- and polyfluoroalkyl substances) are persistent chemicals found in drinking water. The EPA has set enforceable limits for several PFAS compounds under UCMR5 monitoring.

Compliance Snapshot

San Mateo California water systems by violation status, EPA SDWIS records.

No violations on record (2) One or more violations (48)

Violation history is cumulative, many flagged systems have already returned to compliance. Detail pages show per-system context.

Water Systems

System Name Population Violations PFAS
City of Daly City 104,901 12 Clean
California Water Service - San Mateo 102,348 7 Clean
City of Redwood City 92,819 8 Clean
California Water Service-S San Francisco 64,146 8 Clean
California Water Service - Bear Gulch 61,431 9 Clean
City of San Bruno 41,327 2 Clean
North Coast County Water Dist 38,546 5 Clean
Estero Municipal Improvement District 36,556 7 Clean
California Water Service - San Carlos 35,344 8 Clean
City of Burlingame 31,451 9 Clean
Mid-Peninsula Water District 30,609 6 Clean
City of East Palo Alto 29,519 23 Clean
City of Millbrae 22,795 0 Clean
Menlo Park Municipal Water 22,362 3 Clean
Coastside County Water District 18,940 33 Clean
Westborough Water District 13,486 4 Clean
Town of Hillsborough 11,766 5 Clean
Montara Water and Sanitary District 6,078 11 Clean
City of Brisbane 3,402 17 -
Palo Alto Park Mutual Water Company 2,900 9 -
O'Connor Tract Co-Operative Water Co. 2,789 12 -
San Mateo County Memorial Park 1,790 26 -
Guadalupe Valley Mid 1,472 8 Detected
Cuesta la Honda Guild Inc 915 74 -
Csp - Ano Nuevo State Park 709 2 -
Costanoa Campground 583 19 -
County Service Area 11 450 47 -
Camp Jones Gulch 357 8 -
County Service Area 7 300 84 -
Camp Loma Mar 208 69 -
Optimists Volunteers for Youth 207 4 -
Pescadero High School 192 14 -
Csp - Portola State Park 181 32 -
Butano Canyon Mutual 150 49 -
Redwood Glen Camp & Conference Ctr 114 25 -
Harley Farms Goat Dairy 113 0 -
Butano State Park - Csp 95 10 -
Portola Improvement Association MWC 90 53 -
Pigeon Point Hostel 67 7 -
Loma Mar Mutual 65 67 -
Bianchi Flowers Inc 65 9 -
Redwood Terrace Mutual 56 137 -
Marchi Central Farm 50 24 -
Skylawn Memorial Park (Skylawn Inc) 50 131 -
Martins Beach Water System 49 13 -
Oku Incorporated 35 94 -
Uc Elkus Ranch 34 30 -
La Honda Center 33 17 -
Gazos Creek Beach House 33 3 -
San Gregorio Company 32 27 -

Other Counties in California

Los Angeles County
276 systems · 10,109,089 served · 3,972 violations
San Diego County
197 systems · 3,744,323 served · 4,832 violations
Orange County
46 systems · 3,201,893 served · 507 violations
Riverside County
201 systems · 2,839,125 served · 6,103 violations
San Bernardino County
318 systems · 2,830,626 served · 4,611 violations
Alameda County
27 systems · 2,249,634 served · 275 violations

Drinking Water Guides

Frequently Asked Questions

How many water violations are in San Mateo County? ▼
San Mateo County has 1,318 total drinking water violations across 52 water systems, of which 243 are health-based violations. 96.2% of systems have at least one violation.
How many people get water from San Mateo County systems? ▼
Water systems in San Mateo County serve approximately 782,067 people through 52 public water systems.
Has PFAS been detected in San Mateo County water? ▼
Of 19 water systems tested for PFAS in San Mateo County, 4 had PFAS detected (21.1% detection rate).
What types of water sources supply San Mateo County? ▼
Water systems in San Mateo County use SW (34 systems), GW (16 systems) as their primary water sources.
Are health-based violations serious? ▼
Health-based violations indicate that drinking water exceeded Maximum Contaminant Levels (MCLs) set by the EPA or failed treatment technique requirements. 18.4% of San Mateo County's violations are health-based. Not all violations indicate immediate health risk, but they require corrective action.
Data Sources & Methodology

Drinking water violation data from the EPA Safe Drinking Water Information System (SDWIS). PFAS testing data from the UCMR5 monitoring program. SDWIS tracks all public water systems regulated under the Safe Drinking Water Act.

Violations are categorized as health-based (Maximum Contaminant Level exceedances, treatment technique failures) or monitoring/reporting violations. Not all violations indicate an immediate health risk.

Read our methodology - how this data is sourced, computed, and verified.

Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater Editorial

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page draws directly on EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.