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Not health advice. Contact your local water utility for concerns.
Data from EPA Water Quality Reports. For official information, contact your water utility or health department.
Water quality data for 4 cities serving 357,556 residents
San Mateo County in California has an average water quality score of 83/100 (Grade B+) based on analysis of 4 municipal water systems. The county's water systems serve approximately 357,556 residents.
Overall, San Mateo County demonstrates good water quality standards. 1 of 4 cities exceed the county average, with Redwood City leading with a score of 88/100.
4 cities ranked by water quality score
| Rank | City | Score | Grade | Population |
|---|---|---|---|---|
| 1 | Redwood City Top concern: Fluoride (18.2% of limit) | 88 | A- | 80,698 |
| 2 | Daly City Top concern: Haloacetic Acids (20.2% of limit) | 82 | B+ | 104,008 |
| 3 | San Mateo Top concern: Total Trihalomethanes (33.4% of limit) | 81 | B+ | 102,762 |
| 4 | South San Francisco Top concern: Haloacetic Acids (34% of limit) | 81 | B+ | 70,088 |
Top detected contaminants across county water systems
| Contaminant | Avg Level | Max Level | EPA Limit | % of Limit | Cities |
|---|---|---|---|---|---|
| Haloacetic Acids | 15.112 ug/L | 20.396 ug/L | 60 ug/L | 25.2% | 3 |
| Total Trihalomethanes | 15.408 ug/L | 26.706 ug/L | 80 ug/L | 19.3% | 4 |
| Fluoride | 0.717 mg/L | 0.728 mg/L | 4 mg/L | 17.9% | 3 |
| Nitrite | 0.165 mg/L | 0.242 mg/L | 1 mg/L | 16.5% | 4 |
| Chromium | 0.013 mg/L | 0.025 mg/L | 0.1 mg/L | 13.2% | 3 |
| Arsenic | 0.001 mg/L | 0.002 mg/L | 0.01 mg/L | 13% | 3 |
| Mercury | 0 mg/L | 0 mg/L | 0.002 mg/L | 12.5% | 4 |
| Copper | 0.146 mg/L | 0.252 mg/L | 1.3 mg/L | 11.2% | 4 |
Recent violations across county water systems
Water quality in San Mateo County, California reflects the region's unique combination of water sources, treatment infrastructure, and environmental factors. Our comprehensive analysis examines 4 municipal water systems serving a combined population of over 357,556 residents.
The county shows strong water quality performance, with scores ranging from 81/100 in San Mateo to 88/100 in Redwood City. This 7-point spread indicates relatively consistent water quality standards across municipal systems.
The most prevalent contaminants detected across San Mateo County water systems include Haloacetic Acids, Total Trihalomethanes, Fluoride. All monitored contaminants remain within acceptable levels relative to EPA Maximum Contaminant Levels (MCLs).
San Mateo County's water quality is generally good. Residents can feel confident in their tap water quality, though those with specific health concerns or sensitivity to certain contaminants may still benefit from filtration. Regular review of your city's annual Consumer Confidence Report is recommended.
San Mateo County has an average water quality score of 83/100 (Grade B+) based on analysis of 4 municipal water systems serving 357,556 residents.
Redwood City has the highest water quality score in San Mateo County at 88/100. View the detailed report for Redwood City.
Most cities in San Mateo County have water that meets EPA standards. However, a water filter can provide additional protection and improve taste. The need depends on your specific city and any personal health considerations.
Click on any city in the rankings table above to view its detailed water quality report, including contaminant levels, EPA compliance history, and filter recommendations.