Serving roughly 56,538 people in Los Angeles County, California.
Data current as of July 2026
🔍Straight from EPA
🧪Real Lab Results
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Results for GSWC-SAN DIMAS
1 water provider directly on file, serving roughly 56,538 people in Los Angeles County, California.
Quick answer: GSWC-SAN DIMAS has no violations on file. One reading is worth knowing about: Lithium was measured at 57µg/L, among the highest of the 601 providers on file in this area. It's the most notable figure in this system's record among its 601 local peers.
Lead Summary
Lithium
PFOS
Lead
Totalhaloaceticacids (HAA5)
TTHM
Chloroform
Bromodichloromethane
Dibromochloromethane
Bromoform
Dichloroaceticacid
Trichloroaceticacid
Dibromoaceticacid
Monochloroaceticacid
Copper, Free
Utility GSWC-SAN DIMASPopulation served 56,538Owner Private
No violations on file
Contaminants found
Metals
Naturally occurring or corrosion-related elements, e.g. lead, arsenic, copper
Lead Summary
Detected: 0.0021 mg/L (ppm)
12/31/2026
Lead
Detected: 0.63 UG/L (ppb)
9/26/2025
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: 8.7 UG/L (ppb)
9/18/2025
Disinfection Byproducts
Formed when chlorine used to disinfect water reacts with organic matter
Totalhaloaceticacids (HAA5)
Detected: 6.5 UG/L (ppb)
10/23/2025
TTHM
Detected: 36 UG/L (ppb)
10/23/2025
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: 7.3 UG/L (ppb)
10/23/2025
One of the individual trihalomethane disinfection byproducts, formed when chlorine reacts with organic matter.
Bromodichloromethane
Detected: 11 UG/L (ppb)
10/23/2025
Dibromochloromethane
Detected: 12 UG/L (ppb)
10/23/2025
Bromoform
Detected: 5.6 UG/L (ppb)
10/23/2025
PFAS & Emerging Contaminants
Human-made "forever chemicals" and other substances not yet fully regulated
Lithium
Detected: 57 µg/L (ppb)
2/24/2025
Occurs naturally in some groundwater. Not currently federally regulated in drinking water.
PFOS
Detected: 0.0045 µg/L (ppb)
11/18/2024
One of two PFAS with an enforceable federal limit (4 ppt) since 2024.
Other
Additional substances tested that don't fit neatly into the categories above
Dichloroaceticacid
Detected: 1.5 UG/L (ppb)
10/23/2025
Trichloroaceticacid
Detected: 1.7 UG/L (ppb)
10/23/2025
Dibromoaceticacid
Detected: 1.1 UG/L (ppb)
10/23/2025
Monochloroaceticacid
Detected: 3 UG/L (ppb)
4/25/2025
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.