Drinking water quality · 2025
· Verified
What's in California Water Service - San Mateo, CA tap water
13 contaminants were measured in the California Water Service - San Mateo, CA water system's 2025 annual report. Each is shown below against its federal limit.
- Reporting year
- 2025
- Contaminants measured
- 13
- Over federal limit
- 0
- Approaching the limit
- 0
- Service area
- CA
Where your water comes from · EPA SDWIS
California Water Service - San Mateo, CA buys its drinking water from SAN FRANCISCO REGIONAL WATER SYSTEM.
Source
Treatment
Distribution
Also buys water from SAN FRANCISCO REGIONAL WATER SYSTEM.
Historical readings · EPA Six-Year Review (2012–2019)
2 contaminants historically over EPA limits in California Water Service - San Mateo, CA
Every U.S. public water system reports compliance-monitoring data to EPA. The Six-Year Review releases the 2012–2019 window as a single dataset — here's what your system reported, year by year. Values shown are the highest detection per analyte per year, compared to the federal MCL.
| Contaminant | Worst detection | EPA limit | Years (2012–2019) |
|---|---|---|---|
HAA5 worst: 2016 | 0.067 mg/L 1.1× | 0.06 mg/L | '12'13'14'15'16'17'18'19 |
TTHM worst: 2016 | 0.0853 mg/L 1.1× | 0.08 mg/L | '12'13'14'15'16'17'18'19 |
TCAA worst: 2012 | 0.03 mg/L | — | '12'13'14'15'16'17'18'19 |
COPPER worst: 2016 | 0.0764 mg/L below national p90 | — | '16'17'19 |
LEAD worst: 2016 | 0.0147 mg/L | — | '16 |
DBAA worst: 2014 | 0.0014 mg/L | — | '14'15'18 |
DCAA worst: 2012 | 0.029 mg/L | — | '12'13'14'15'16'17'18'19 |
MBAA worst: 2013 | 0.0011 mg/L | — | '13 |
MCAA worst: 2012 | 0.0024 mg/L | — | '12'13'14'16'17'18'19 |
BROMODICHLOROMETHANE worst: 2012 | 0.0026 mg/L | — | '12'13'14'15'16'17'18'19 |
BROMOFORM worst: 2012 | 0.00052 mg/L | — | '12'14'15'18 |
CHLOROFORM worst: 2012 | 0.0428 mg/L | — | '12'13'14'15'16'17'18'19 |
DIBROMOCHLOROMETHANE worst: 2012 | 0.00117 mg/L | — | '12'13'14'15'16'17'18'19 |
People also ask about California Water Service - San Mateo, CA's water
+Is California Water Service - San Mateo, CA tap water safe to drink in 2025?
Every one of the 13 contaminants measured in California Water Service - San Mateo, CA's 2025 Consumer Confidence Report is below its federal limit. "Safe" under the EPA's drinking-water standards is health-based, not aesthetic — but by those standards, no measured contaminant in this report exceeds its enforceable threshold. Individual health concerns (e.g. immunocompromised, infant, pregnancy) may warrant additional filtering regardless of compliance.
+What contaminants are in California Water Service - San Mateo, CA tap water?
13 contaminants were measured in California Water Service - San Mateo, CA's 2025 Consumer Confidence Report, spanning disinfection byproducts, other, and metals. 4 have an enforceable federal limit; the rest are detected but unregulated. Every measured value, in the utility's own units, is on this page.
+Where does the data on this page come from?
Every value is transcribed from California Water Service - San Mateo, CA's 2025 Consumer Confidence Report — the annual drinking-water report every U.S. public water utility is required by federal law to publish. The original source document is archived and viewable on this site. A water-quality report covers an entire service area, not a single address.
+How often is California Water Service - San Mateo, CA's water quality data updated?
Each U.S. public water utility publishes one Consumer Confidence Report per year, covering the prior calendar year's measurements. This page reflects the 2025 report; a new report will replace it once the utility publishes its next annual update.