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.
Compliance history
Federal Safe Drinking Water Act violation & enforcement records (EPA SDWIS). A violation is a regulatory determination by the state or EPA — separate from the measured levels above.
- Treatment technique violationHealth-based1 violation on record · most recent Jun 1993resolved
- Maximum contaminant level exceededHealth-based1 violation on record · most recent Oct 1992resolved
Source: EPA SDWIS / ECHO. View the full federal record on EPA ECHO ↗
Disinfectants
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| ChloramineA longer-lasting disinfectant made by combining chlorine with ammonia. | 2.8 mg/LAverageSystem-wide | 4 mg/LMCL | Within the limit |
Disinfection byproducts
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| HAA5Haloacetic acids — a group of five disinfection byproducts formed when disinfectants react with organic matter. | 40 ug/LAverageAnnual Average | None set | Within the limit |
| TTHMTotal trihalomethanes — a group of four chemicals (including chloroform) formed when chlorine reacts with natural organic matter. | 41 ug/LAverageAnnual Average | None set | Within the limit |
| ChlorateA byproduct that can form during disinfection, especially when hypochlorite solutions degrade. | 144 ug/LAverageSFPUC Water | 800 ug/LNL | Detected — no federal limit |
Physical & aggregate
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| TurbidityA measure of cloudiness from suspended particles in the water. | 0.4 NTUMaximumSFPUC Water | None set | 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 |
| Specific ConductanceA measure of how well water conducts electricity, which tracks dissolved mineral content. | 193AverageSFPUC Water | 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 |
| Total Dissolved SolidsTotal dissolved solids — the combined content of all dissolved minerals and salts. | 102 mg/LAverageSFPUC Water | None set | Detected — no federal 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 | 4 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 |
| ChlorideA naturally occurring salt compound. | 9.3 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| SulfateA naturally occurring mineral from rock and soil. | 18 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
Metals
| Contaminant | Measured | Federal limit | Status |
|---|---|---|---|
| CopperA metal that enters water from corroding household plumbing. | Not detected mg/L90th percentileAt the tap | 1.3 mg/LAction level | None detected |
| LeadA toxic metal that leaches into water from old service lines, solder, and plumbing fixtures. | Not detected ug/L90th percentileAt the tap | None set | None detected |
| AluminumA common element sometimes used as a treatment coagulant. | Not detected mg/LAverageSystem-wide | None set | Detected — no federal limit |
| BoronA naturally occurring element from rock and soil. | 0.04 mg/LAverageSFPUC Water | 1 mg/LNL | Detected — no federal limit |
| CalciumA naturally occurring mineral that contributes to water hardness. | 15 mg/LAverageSFPUC Water | None set | Detected — no federal limit |
| Chromium, HexavalentHexavalent chromium ('chromium-6') — the more toxic form of chromium. | 0.1 ug/LAverageSystem-wide | None set | Detected — no federal limit |
| IronA naturally occurring metal common in groundwater. | 14 ug/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 |
| ManganeseA naturally occurring metal from soil and rock. | Not detected ug/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 | None set | 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. 7 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.