Tap Water Results

Is Cupertino, 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 Los Altos Suburban. 1 PFAS were detected below the limits.

3 public water systems serve parts of Cupertino. The largest, California Water Service Los Altos Suburban, serves 63,559 people. Your water bill names your system.

Largest system

California Water Service Los Altos Suburban

63,559 people · Purchased surface water · EPA ID CA4310001

Buys treated water from Purissima Hills Water District, Santa Clara Valley Water District.

PFASHighest averageLimitStatus
PFOA
Not detected
–4 pptNot detected
PFOS
Not detected
–4 pptNot detected
PFHxS
Detected, below limit
1.75 ppt10 pptDetected, below limit
PFNA
Not detected
–10 pptNot detected
HFPO-DA (GenX)
Not detected
–10 pptNot detected

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: 1.5 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

Full California Water Service Los Altos Suburban results

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.

Cupertino homes and lead pipes

64%
of homes built before 1980 (California 56%, US 50%)
3%
built before 1950 (California 14%)
39%
of households rent (California 44%)

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 Cupertino city (tables B25034, B25003). Estimates for small places have a margin of error.

Other water systems serving Cupertino

How nearby cities compare

CityMain water systemPFASLead (90th pct.)
Los Altos 4 mi
California Water Service Los Altos Suburban
California Water Service Los Altos SuburbanNone above limits1.5 ppb
Sunnyvale 5 mi
City of Sunnyvale
City of SunnyvaleNone above limits0 ppb
Santa Clara 5 mi
City of Santa Clara
City of Santa ClaraNone above limits2.7 ppb
Mountain View 6 mi
City of Mountain View
City of Mountain ViewNone above limits0 ppb
Palo Alto 8 mi
City of Palo Alto
City of Palo AltoNone above limits0 ppb
Los Gatos 8 mi
San Jose Water
San Jose WaterNone above limits0 ppb
Cupertino ZIP codes (1)
  • 95014

Questions

Is Cupertino tap water safe to drink?

California Water Service Los Altos Suburban 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 Cupertino, CA?

3 public water systems serve parts of Cupertino. The largest is California Water Service Los Altos Suburban (63,559 people). Your water bill names your system. The EPA ID is also on your utility's Consumer Confidence Report.

Does Cupertino tap water have PFAS?

California Water Service Los Altos Suburban had 1 PFAS detected at least once in EPA's 2023–2025 testing, all with averages below the federal limits.

Do Cupertino homes have lead pipes?

Census estimates put 64% of Cupertino 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 Los Altos Suburban'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.