Is Foster City, 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 – San Mateo.
2 public water systems serve parts of Foster City. The largest, California Water Service – San Mateo, serves 103,536 people. Your water bill names your system.
Largest system
California Water Service – San Mateo
103,536 people · Purchased surface water · EPA ID CA4110008
Buys treated water from San Francisco Regional Water System.
| 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: 4.4 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.
Foster City 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 Foster City city (tables B25034, B25003). Estimates for small places have a margin of error.
Other water systems serving Foster City
- Estero Municipal Improvement District36,556 people · Purchased surface water · California · reported ZIPs hereNo PFAS above limits
How nearby cities compare
| City | PFAS | Lead (90th pct.) |
|---|---|---|
| San Mateo 3 mi California Water Service – San Mateo | None above limits | 4.4 ppb |
| Redwood City 4 mi City of Redwood City | None above limits | 0 ppb |
| Belmont 4 mi California Water Service – San Mateo | None above limits | 4.4 ppb |
| San Carlos 5 mi California Water Service – San Carlos | None above limits | 5.8 ppb |
| Burlingame 6 mi City of Burlingame | None above limits | 6.3 ppb |
| Menlo Park 8 mi California Water Service – Bear Gulch | None above limits | 4 ppb |
Foster City ZIP codes (1)
- 94404
Questions
Is Foster City tap water safe to drink?
California Water Service – San Mateo 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 Foster City, CA?
2 public water systems serve parts of Foster City. The largest is California Water Service – San Mateo (103,536 people). Your water bill names your system. The EPA ID is also on your utility's Consumer Confidence Report.
Does Foster City tap water have PFAS?
None detected above EPA's reporting limits. California Water Service – San Mateo 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 Foster City homes have lead pipes?
Census estimates put 66% of Foster City 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 – San Mateo'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.