Drinking water quality · 2024
· Verified
What's in San Mateo, CA tap water
30 contaminants were measured in the San Mateo, CA water system's 2024 annual report. Each is shown below against its federal limit.
- Reporting year
- 2024
- Contaminants measured
- 30
- Over federal limit
- 0
- Approaching the limit
- 0
- Service area
- CA
Where your water comes from · EPA SDWIS
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 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 |
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 |
TCAA worst: 2012 | 0.03 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 |
Disinfectants
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| ChloramineA longer-lasting disinfectant made by combining chlorine with ammonia. | 2.8 mg/LAverageSystem-wide | 4 mg/LMRDL | Within the limit |
Inorganic chemicals
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| FluorideA mineral often added to drinking water to help prevent tooth decay. | 0.7 mg/LAverageSystem-wide | 2 mg/LMCL | Within the limit |
| SulfateA naturally occurring mineral from rock and soil. | 18 mg/LAverageSFPUC Water | 500 mg/LMCL | Within the limit |
| ChlorideA naturally occurring salt compound. | 9.3 mg/LAverageSFPUC Water | 500 mg/LMCL | Within the limit |
| NitrateA compound from fertilizer runoff, septic systems, and erosion of natural deposits. | Not detected mg/LAverageSystem-wide | 10 mg/LMCL | Within the limit |
| BromideA naturally occurring salt found in source water. | Not detected ug/LAverageSFPUC Water | None set | Detected — no federal limit |
Disinfection byproducts
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| ChlorateA byproduct that can form during disinfection, especially when hypochlorite solutions degrade. | 144 ug/LAverageSFPUC Water | 800 ug/LNL | Within the limit |
Physical & aggregate
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| Specific ConductanceA measure of how well water conducts electricity, which tracks dissolved mineral content. | 193AverageSFPUC Water | 1600MCL | Within the limit |
| Total Dissolved SolidsTotal dissolved solids — the combined content of all dissolved minerals and salts. | 102 mg/LAverageSFPUC Water | 1000 mg/LMCL | Within the limit |
| AlkalinityA measure of the water's capacity to neutralize acids. | 60 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| HardnessA measure of dissolved calcium and magnesium minerals. | 60 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| pHA measure of how acidic or basic the water is. | 8.9AverageDistribution System-Wide | None set | Detected — no federal limit |
| TOCTotal organic carbon — a measure of organic material dissolved in the water. | 1.5 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| TurbidityA measure of cloudiness from suspended particles in the water. | 0.4 NTUMaximumSFPUC Water | None set | Detected — no federal limit |
Metals
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| IronA naturally occurring metal common in groundwater. | 14 ug/LAverageSFPUC Water | 300 ug/LMCL | Within the limit |
| BoronA naturally occurring element from rock and soil. | 0.04 mg/LAverageSFPUC Water | 1 mg/LNL | Within the limit |
| Chromium, HexavalentHexavalent chromium ('chromium-6') — the more toxic form of chromium. | 0.1 ug/LAverageSystem-wide | 10 ug/LMCL | Within the limit |
| AluminumA common element sometimes used as a treatment coagulant. | Not detected ug/LAverageSFPUC Water | 200 ug/LMCL | Within the limit |
| ManganeseA naturally occurring metal from soil and rock. | Not detected ug/LAverageSFPUC Water | 50 ug/LMCL | Within the limit |
| CalciumA naturally occurring mineral that contributes to water hardness. | 15 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| LithiumA naturally occurring element found in some groundwater. | Not detected mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| MagnesiumA naturally occurring mineral that contributes to water hardness. | 5.7 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| SilicaA naturally occurring compound from sand and rock. | 7.5 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| SodiumA naturally occurring salt component. | 16 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
Microbial
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| Escherichia coli (E. coli)Escherichia coli — bacteria found in the gut of humans and animals. | 0MaximumMonthly | 0MCL | None detected |
| Giardia lamblia | 0.02AverageSFPUC Water | 0Public health goal | Detected — no federal limit |
People also ask about San Mateo, CA's water
+Is San Mateo, CA tap water safe to drink in 2024?
Every one of the 30 contaminants measured in San Mateo, CA's 2024 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 San Mateo, CA tap water?
30 contaminants were measured in San Mateo, CA's 2024 Consumer Confidence Report, spanning metals, physical & aggregate, and inorganic chemicals. 19 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 San Mateo, CA's 2024 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 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 2024 report; a new report will replace it once the utility publishes its next annual update.