Serving roughly 43,176 people in Los Angeles County, California.
Data current as of July 2026
🔍Straight from EPA
🧪Real Lab Results
📅Updated Quarterly
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Results for GSWC - NORWALK
1 water provider directly on file, serving roughly 43,176 people in Los Angeles County, California.
Quick answer: GSWC - NORWALK has no violations on file. One reading is worth knowing about: Perfluoroheptanoicacid (PFHPA) was measured at 4.9NG/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
PFBA
PFPEA
PFHXA
Totalhaloaceticacids (HAA5)
TTHM
Chloroform
Bromoform
Bromodichloromethane
Dibromochloromethane
Dichloroaceticacid
Trichloroaceticacid
Dibromoaceticacid
Copper, Free
Perfluoroheptanoicacid (PFHPA)
Perfluoroctanoicacid (PFOA)
Perfluorohexanoicacid (PFHXA)
Perfluorobutanoicacid (PFBA)
Perfluoropentanoicacid (PFPEA)
Perfluorobutanesulfonicacid (PFBS)
Perfluorohexanesulfonicacid (PFHxS)
Perfluoroctanesulfonicacid (PFOS)
Perfluoropentanesulfonicacid (PFPES)
Manganese
Trichloroethylene
1, 1-Dichloroethylene
Utility GSWC - NORWALKPopulation served 43,176Owner Private
No violations on file
Contaminants found
Metals
Naturally occurring or corrosion-related elements, e.g. lead, arsenic, copper
Lead Summary
Detected: 0 mg/L (ppm)
12/31/2025
Copper, Free
Detected: 220 UG/L (ppb)
9/18/2025
Manganese
Detected: 11 UG/L (ppb)
10/8/2025
Mainly a taste/staining concern at typical levels; long-term neurological research at high chronic exposure is ongoing.
Disinfection Byproducts
Formed when chlorine used to disinfect water reacts with organic matter
Totalhaloaceticacids (HAA5)
Detected: 8.1 UG/L (ppb)
8/6/2025
TTHM
Detected: 16 UG/L (ppb)
8/6/2025
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: 2.5 UG/L (ppb)
8/6/2025
One of the individual trihalomethane disinfection byproducts, formed when chlorine reacts with organic matter.
Bromoform
Detected: 2.4 UG/L (ppb)
8/6/2025
Bromodichloromethane
Detected: 4.4 UG/L (ppb)
8/6/2025
Dibromochloromethane
Detected: 7 UG/L (ppb)
8/6/2025
PFAS & Emerging Contaminants
Human-made "forever chemicals" and other substances not yet fully regulated
Lithium
Detected: 58 µg/L (ppb)
4/4/2024
Occurs naturally in some groundwater. Not currently federally regulated in drinking water.
PFBA
Detected: 0.0073 µg/L (ppb)
3/13/2024
PFPEA
Detected: 0.015 µg/L (ppb)
3/13/2024
PFHXA
Detected: 0.013 µg/L (ppb)
3/13/2024
VOCs (Volatile Organic Compounds)
Industrial solvents and fuel-related chemicals that evaporate easily
Trichloroethylene
Detected: 1.2 UG/L (ppb)
8/5/2025
1, 1-Dichloroethylene
Detected: 2.2 UG/L (ppb)
7/22/2025
Other
Additional substances tested that don't fit neatly into the categories above
Dichloroaceticacid
Detected: 1.6 UG/L (ppb)
8/6/2025
Trichloroaceticacid
Detected: 1.1 UG/L (ppb)
8/6/2025
Dibromoaceticacid
Detected: 5.8 UG/L (ppb)
8/6/2025
Perfluoroheptanoicacid (PFHPA)
Detected: 4.9 NG/L (ppt)
10/7/2025
Perfluoroctanoicacid (PFOA)
Detected: 2.7 NG/L (ppt)
10/8/2025
One of two PFAS with an enforceable federal limit (4 ppt) since 2024.
Perfluorohexanoicacid (PFHXA)
Detected: 2.8 NG/L (ppt)
10/8/2025
Perfluorobutanoicacid (PFBA)
Detected: 6.5 NG/L (ppt)
10/8/2025
Perfluoropentanoicacid (PFPEA)
Detected: 5.3 NG/L (ppt)
10/8/2025
Perfluorobutanesulfonicacid (PFBS)
Detected: 3.1 NG/L (ppt)
10/8/2025
Perfluorohexanesulfonicacid (PFHxS)
Detected: 3.2 NG/L (ppt)
10/8/2025
Perfluoroctanesulfonicacid (PFOS)
Detected: 2.3 NG/L (ppt)
10/8/2025
One of two PFAS with an enforceable federal limit (4 ppt) since 2024.
Perfluoropentanesulfonicacid (PFPES)
Detected: 2 NG/L (ppt)
1/10/2025
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.