- EPA's UCMR 5 testing looked for 30 contaminants here and found 3.
- Lithium: found in 4 of 20 samples, average 7.8 µg/L, highest 57 µg/L (EPA UCMR 5 testing, Nov 2024–Aug 2025)
- PFBA (a PFAS): found in 3 of 20 samples, average 2.2 ppt, highest 20 ppt (EPA UCMR 5 testing, Nov 2024–Aug 2025)
- PFOS (a PFAS): found in 2 of 20 samples, average 0.50 ppt, highest 4.6 ppt (EPA UCMR 5 testing, Nov 2024–Aug 2025)
- Lead, 90th percentile: 2.1 ppb at the latest result in EPA records for a monitoring period that ran on or after July 1, 2021, at or below EPA's 15 ppb action level (EPA SDWIS, monitoring period Jan 1, 2024–Dec 31, 2026). The 90th percentile is a system-wide measure from homes sampled under EPA's lead rule; it isn't a result for your home.
Public EPA test results
Can you drink San Dimas tap water? What EPA records show
EPA CA1910142 · serves Los Angeles County, CA · about 56,564 people (EPA SDWIS)
This report shows EPA's federal records for this water system: UCMR 5 testing, lead testing and violations. It isn't a test of the water at your tap, and it has no Water Score.
Public EPA test results
Gswc-San Dimas (EPA CA1910142)
ScoreYourWater.com gives no verdict on your tap water; it shows what the public records say, as of October 14, 2026. For San Dimas's main utility, Gswc-San Dimas: We found no health-based violations in EPA's records for this system (CA1910142) since July 1, 2021, as of October 14, 2026. EPA's UCMR 5 testing looked for 30 contaminants here and found 3.
What EPA records show for Gswc-San Dimas, as of October 14, 2026
We found no health-based violations in EPA's records for this system (CA1910142) since July 1, 2021, as of October 14, 2026.
Source: EPA ECHO record for Gswc-San Dimas (SDWIS). Data as of October 14, 2026.
Lead, 90th percentile: 2.1 ppb at the latest result in EPA records for a monitoring period that ran on or after July 1, 2021, at or below EPA's 15 ppb action level (EPA SDWIS, monitoring period Jan 1, 2024–Dec 31, 2026). The 90th percentile is a system-wide measure from homes sampled under EPA's lead rule; it isn't a result for your home.
EPA's UCMR 5 testing looked for 30 contaminants here and found 3.
Source: EPA records (SDWIS, UCMR 5). SDWIS: data as of Oct 14, 2026. EPA UCMR 5 data, samples through June 2026.
Your water bill names your utility.
Does Gswc-San Dimas use chloramine?
We didn't find chloramine in Gswc-San Dimas's EPA treatment records. That's not a complete list; your utility's annual water quality report says which disinfectant it uses.