Is South San Francisco, CA tap water safe?
Data: U.S. EPA · How we read the data · How we check it
Summary
No federal limits exceeded in EPA data for California Water Service – South San Francisco.
2 public water systems serve parts of South San Francisco. The largest, California Water Service – South San Francisco, serves 62,609 people. Your water bill names your system.
Largest system
California Water Service – South San Francisco
62,609 people · Purchased surface water · EPA ID CA4110009
Buys treated water from San Francisco Regional Water System, City of Brisbane.
| PFAS | Highest average | Limit |
|---|---|---|
| PFOA Not detected | – | 4 ppt |
| PFOS Not detected | – | 4 ppt |
| PFHxS Not detected | – | 10 ppt |
| PFNA Not detected | – | 10 ppt |
| HFPO-DA (GenX) Not detected | – | 10 ppt |
ppt = parts per trillion. "Highest average" is the highest average at any of the system's entry points, the way EPA compares results with the limits.
Lead: 4.1 ppb at the 90th percentile (Dec 2025, and 9 in 10 homes sampled were at or below it) Below action level
Health-based violations since 2016: 0
Across California, 129 of 691 water systems EPA tested had PFAS above a 2024 federal limit, and 26 systems were above the lead action level in results from the last five years. California results.
South San Francisco homes and lead pipes
Lead service lines and lead solder were allowed until 1986, so homes from before then are the ones to check. Renting? Ask your landlord what the service line is made of, because it's their pipe to replace. How to check your own line.
Housing: Census American Community Survey 2020–2024 5-year estimates for South San Francisco city (tables B25034, B25003). Estimates for small places have a margin of error.
Other water systems serving South San Francisco
- Westborough Water District13,486 people · Purchased surface water · California · reported ZIPs hereNo PFAS above limits
How nearby cities compare
| City | PFAS | Lead (90th pct.) |
|---|---|---|
| San Bruno 4 mi California Water Service – South San Francisco | None above limits | 4.1 ppb |
| Burlingame 5 mi City of Burlingame | None above limits | 6.3 ppb |
| Daly City 5 mi City of Daly City | None above limits | 0 ppb |
| Pacifica 6 mi North Coast County Water District | None above limits | 0 ppb |
| San Mateo 7 mi California Water Service – San Mateo | None above limits | 4.4 ppb |
| Alameda 9 mi East Bay Municipal Utility District | None above limits | 0 ppb |
South San Francisco ZIP codes (1)
- 94080
Questions
Is South San Francisco tap water safe to drink?
California Water Service – South San Francisco has had no health-based violations since 2016. Utility data can't show lead from your own pipes: if your home was built before 1986, test your tap. Your utility's annual Consumer Confidence Report is the official summary.
Who supplies water in South San Francisco, CA?
2 public water systems serve parts of South San Francisco. The largest is California Water Service – South San Francisco (62,609 people). Your water bill names your system. The EPA ID is also on your utility's Consumer Confidence Report.
Does South San Francisco tap water have PFAS?
None detected above EPA's reporting limits. California Water Service – South San Francisco had no PFAS detected in EPA's 2023–2025 testing. "Not detected" means below the reporting limit (about 2 to 20 ppt), not proven zero.
Do South San Francisco homes have lead pipes?
Census estimates put 70% of South San Francisco homes as built before 1980 (California: 56%). Lead service lines and lead solder were allowed until 1986, so older homes are more likely to have them. California Water Service – South San Francisco's service line inventory says what your line is made of. The only way to know for your home is to check the line where it enters the house and test your tap.
Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.