CALIFORNIA WATER SERVICE - SAN MATEO Water Quality Report
Serving roughly 102,348 people in San Mateo County, California.
Data current as of July 2026
🔍Straight from EPA
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Results for CALIFORNIA WATER SERVICE - SAN MATEO
1 water provider directly on file, serving roughly 102,348 people in San Mateo County, California.
Quick answer: CALIFORNIA WATER SERVICE - SAN MATEO has no violations on file and no single reading stands out against its peers (113 other providers in this area). It serves roughly 102,348 people, and the full breakdown below reflects everything EPA and California have on record for it.
Lead Summary
Lead
Totalhaloaceticacids (HAA5)
TTHM
Chloroform
Bromodichloromethane
Dibromochloromethane
Dichloroaceticacid
Trichloroaceticacid
Monochloroaceticacid
Copper, Free
Utility CALIFORNIA WATER SERVICE - SAN MATEOPopulation served 102,348Owner Private
No violations on file
Contaminants found
Metals
Naturally occurring or corrosion-related elements, e.g. lead, arsenic, copper
Lead Summary
Detected: 0.0044 mg/L (ppm)
12/31/2025
Lead
Detected: 8.9 UG/L (ppb)
6/12/2025
A metal that can leach from old pipes, solder, and fixtures. Current medical guidance holds there is no truly safe level of lead exposure, especially for children and pregnant women.
Copper, Free
Detected: 29.5 UG/L (ppb)
6/12/2025
Disinfection Byproducts
Formed when chlorine used to disinfect water reacts with organic matter
Totalhaloaceticacids (HAA5)
Detected: 42 UG/L (ppb)
8/7/2025
TTHM
Detected: 54 UG/L (ppb)
8/7/2025
A group of disinfection byproducts formed when chlorine reacts with organic matter. Long-term exposure above the legal limit has been linked to increased cancer risk in some studies.
Chloroform
Detected: 53 UG/L (ppb)
8/7/2025
One of the individual trihalomethane disinfection byproducts, formed when chlorine reacts with organic matter.
Bromodichloromethane
Detected: 0.95 UG/L (ppb)
8/7/2025
Dibromochloromethane
Detected: 2.1 UG/L (ppb)
2/4/2025
Other
Additional substances tested that don't fit neatly into the categories above
Dichloroaceticacid
Detected: 23 UG/L (ppb)
8/7/2025
Trichloroaceticacid
Detected: 16 UG/L (ppb)
8/7/2025
Monochloroaceticacid
Detected: 2.4 UG/L (ppb)
8/7/2025
Filtration considerations: See the table below for how whole-house carbon, under-sink reverse osmosis, and under-sink carbon systems compare against what's actually on file here. These are general system types, not a specific product recommendation.