- EPA's UCMR 5 testing looked for 30 contaminants here and found 1.
- Lithium: found in 2 of 6 samples, average 6.93 µg/L, highest 23.6 µg/L (EPA UCMR 5 testing, Jun 2024–Mar 2025)
- Lead, 90th percentile: 4.1 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, 2023–Dec 31, 2025). 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
What EPA records show for California Water Service-S San Francisco
EPA CA4110009 · serves San Mateo County, CA · about 62,609 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
California Water Service-S San Francisco (EPA CA4110009)
What EPA records show for California Water Service-S San Francisco, as of October 14, 2026
We found no health-based violations in EPA's records for this system (CA4110009) since July 1, 2021, as of October 14, 2026.
Source: EPA ECHO record for California Water Service-S San Francisco (SDWIS). Data as of October 14, 2026.
Lead, 90th percentile: 4.1 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, 2023–Dec 31, 2025). 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 1.
PFOA and PFOS were not detected at or above EPA's reporting level in EPA's UCMR 5 testing.
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 California Water Service-S San Francisco use chloramine?
EPA treatment records (state-reported) list chloramines for California Water Service-S San Francisco. EPA record
What EPA records show for this system
Reported results in EPA records (data as of Oct 14–15, 2026)