Is Los Altos, CA tap water safe?
Supplied by California Water Service Los Altos Suburban · serves 63,559 people (18,530 connections) · Purchased surface water · EPA ID CA4310001
Data: U.S. EPA · How we read the data · How we check it
Buys water from Purissima Hills Water District, Santa Clara Valley Water District. Treated water bought from another system can carry that system's contaminants.
Summary
No federal limits exceeded in EPA data.
- PFAS
- Detected, below limit1 of 29 PFAS found at least once. All averages below the federal limits.
- Lead
- Below action level1.5 ppb (parts per billion) at the 90th percentile: 9 in 10 homes sampled were at or below it. Action level 15 ppb, falling to 10 ppb in Nov 2027. Monitoring period ending Dec 2025. Your home's pipes can make yours higher.
- Violations
- None health-basedNo health-based violations since 2016.
- Built before 1986, or not sure what your service line is made of? Check your service line and test your tap. Utility data can't show your pipes.
- Want to reduce what was found? Filters for these results.
- Tested your own tap? Compare your result with these numbers. Moving? Compare this system with another.
- Read California Water Service Los Altos Suburban's annual water quality report (Consumer Confidence Report). It lists every regulated contaminant tested and is usually on the utility's website or mailed with your bill, and you can also request it at (408) 367-8593. EPA: how to find it.
PFAS (“forever chemicals”)
EPA UCMR 5: 16 entry points tested Jun 2023 to Mar 2025. "Average" is the highest entry-point average (non-detects counted as zero), the way EPA compares UCMR 5 results to the limits. ppt = parts per trillion. These results do not determine compliance.
| Contaminant | Highest average |
|---|---|
| PFOA Not detected Limit 4 ppt | – |
| PFOS Not detected Limit 4 ppt | – |
| PFHxS Detected, below limit Limit 10 ppt | 1.75 ppt 18% of the limit |
| PFNA Not detected Limit 10 ppt | – |
| HFPO-DA (GenX) Not detected Limit 10 ppt | – |
| Hazard Index (a combined score for PFHxS, PFNA, GenX and PFBS, where above 1 is over the limit) Detected, below limit Limit 1 | 0.17 |
| PFBS Not detected Guideline 2,000 ppt | – |
| PFBA Not detected Guideline 6,000 ppt | – |
| PFHxA Not detected Guideline 3,000 ppt | – |
29 PFAS tested, 1 detected at least once. "Not detected" means below EPA's reporting limit (about 2 to 20 ppt depending on the chemical), not proven zero. PFAS not listed were not detected. The limits for PFHxS, PFNA, GenX and the Hazard Index were proposed for rescission in May 2026. That proposal is not final. Systems have until 2029 to meet the limits.
Lithium
Not detected in 36 samples (reporting limit 9 ppb). About lithium.
Lead and copper
Latest 90th percentile: 1.5 ppb lead (Jan 2023 – Dec 2025). Below action level
Highest since 2016: 2.5 ppb (Dec 2022).
| Monitoring period | Lead (90th pct.) |
|---|---|
| Jan 2023 – Dec 2025 | 1.5 ppb |
| Jan 2020 – Dec 2022 | 2.5 ppb |
| Jan 2017 – Dec 2019 | 0 ppb |
Earlier results (9)
| Jan 2016 – Dec 2018 | 0 ppb |
| Jan 2013 – Dec 2015 | 0 ppb |
| Jan 2010 – Dec 2010 | 0 ppb |
| Jan 2005 – Dec 2007 | 0 ppb |
| Jan 2002 – Dec 2004 | 0 ppb |
| Jan 2001 – Dec 2003 | 0 ppb |
| Jan 2001 – Dec 2001 | 5 ppb |
| Jan 1999 – Dec 2001 | 0 ppb |
| Jan 1998 – Dec 1998 | 5 ppb |
Lead comes from pipes and fixtures, not the source water, so it varies home to home. The 90th percentile means 9 in 10 sampled homes were at or below it. More on lead.
Violations
Health-based violations mean a contaminant exceeded a limit or a required treatment step was missed. Monitoring and reporting violations mean required tests or reports were late or missing, so the water's quality during that time is unknown. The total includes every violation in EPA's records, most of them paperwork.
Earlier EPA testing (2013–2020)
| Contaminant | Highest | Guideline |
|---|---|---|
| Manganese | 9.6 ppb | 300 ppb |
| Molybdenum | 4.5 ppb | 40 ppb |
| Strontium | 1.1 ppm | 1.5 ppm |
| Chromium-6 | 2.6 ppb | – |
| Chlorate | 450 ppb | 210 ppb |
| Cobalt | 1.1 ppb | 70 ppb |
| Vanadium | 19 ppb | 21 ppb |
Where it serves
Los Altos, Sunnyvale, Santa Clara, Mountain View, Cupertino, Los Altos Hills
ZIP codes the system reported serving: 94022, 94024, 94040, 94041, 94086, 94087, 94306, 95014, 95051
Nearby utilities
- City of Mountain View Mountain View · 2 mi
- California Water Service – Bear Gulch Palo Alto · 3 mi
- City of Palo Alto Palo Alto · 3 mi
- City of Sunnyvale Sunnyvale · 4 mi
- City of Santa Clara Santa Clara · 7 mi
- City of Redwood City Redwood City · 12 mi
Questions
Is Los Altos tap water safe to drink?
Most of Los Altos gets its water from California Water Service Los Altos Suburban. California Water Service Los Altos Suburban has no health-based violations since 2016. EPA testing found no PFAS above the federal limits. Federal data can't tell you about your own pipes: lead comes from service lines and plumbing, so test your tap if your home was built before 1986. For the official word, read the utility's annual Consumer Confidence Report.
Does Los Altos water have PFAS?
Yes. EPA's 2023–2025 testing of California Water Service Los Altos Suburban found 1 PFAS at least once. None of the averages were above the federal limits.
What is the lead level in Los Altos water?
The most recent 90th-percentile lead result for California Water Service Los Altos Suburban is 1.5 ppb, for the period ending Dec 2025. The federal action level is 15 ppb, falling to 10 ppb in November 2027. The 90th percentile means 9 in 10 homes sampled were at or below this number. Individual homes can be higher.
Check these numbers yourself
Every figure on this page comes from public EPA records. You don't have to take our word for it:
- EPA's own report for CA4310001: violations, enforcement and inspections, straight from EPA.
- EPA UCMR 5 data: the PFAS and lithium results (search the file for PWSID CA4310001).
- EPA SDWIS download: the lead results, population and violation records we use.
- The utility's annual water quality report (Consumer Confidence Report): ask California Water Service Los Altos Suburban at (408) 367-8593, or see EPA's guide to finding it.
Found something that doesn't match? Tell us and we'll check it against EPA's records. How we check our data.
Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.