Santa Clara County tap water: hardness, PFAS and lead
Santa Clara County, California has about 1,926,325 residents (Census 2024 estimate) and 73 community water systems in EPA records. The largest local system is San Jose Water, serving about 1,039,920 people from surface water.
! 1 of 6 largest systems with health-based violationsPFAS detected at 2 of 6 sampled systemsHardness 77–451 mg/L, varies by area
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
How hard is Santa Clara County water?
San Jose WaterMeasured (utility report, 2025) · High confidence
77–451 mg/L(varies by area; no single average published)
Mountain Surface Water: 151 mg/L (8.8 gpg)
Groundwater: 288 mg/L (16.8 gpg), range 175–451 mg/L
Valley Water Surface Water: 99 mg/L (5.8 gpg), range 77–146 mg/L
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
Softener size at 16.8 gpg
For a 3-person home using 57 gallons per person per day and regenerating weekly, you'd remove about 20,110 grains between regenerations. Suggested size: 24,000 grain. Hardness varies by area here, so this uses the harder plant's figure (16.8 gpg). If your address gets softer water, a smaller unit may do; check your area in the utility report or test your tap.
Estimate only. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
The 6 biggest of 73 community water systems on EPA records for this county. Service areas don't follow county lines; your water bill names your provider.
San Jose Water
CA4310011 · serves about 1,039,920 people · Surface water
! 1 health-based violation✓ Lead below detectionPFAS detected (2 types)
Lead 90th percentile: <DL (below the lab detection/reporting limit; reported as 0) (period starting 2023-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
PFOS: highest sample 6.2 ppt (2 of 37 samples); federal limit 4.0 ppt as a running annual average
PFHxS: highest sample 5.5 ppt (12 of 36 samples); federal limit 10.0 ppt as a running annual average, also counted in EPA's PFAS mixture (hazard index) limit (currently in effect; EPA has proposed removing it)
CA4310014 · serves about 157,566 people · Surface water
✓ No health-based violations✓ Lead below detection✓ No PFAS detected
Lead 90th percentile: <DL (below the lab detection/reporting limit; reported as 0) (period starting 2023-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
CA4310022 · serves about 112,582 people · Groundwater
✓ No health-based violations✓ Lead below detectionPFAS detected (4 types)
Lead 90th percentile: <DL (below the lab detection/reporting limit; reported as 0) (period starting 2024-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
PFHxS: highest sample 8 ppt (5 of 38 samples); federal limit 10.0 ppt as a running annual average, also counted in EPA's PFAS mixture (hazard index) limit (currently in effect; EPA has proposed removing it)
PFPeA: highest sample 4.7 ppt (5 of 38 samples); no federal limit
PFOS: highest sample 4.6 ppt (1 of 38 samples); federal limit 4.0 ppt as a running annual average
PFHxA: highest sample 4.5 ppt (5 of 38 samples); no federal limit
CA4310020 · serves about 99,783 people · Surface water
✓ No health-based violations✓ Lead below detection✓ No PFAS detected
Lead 90th percentile: <DL (below the lab detection/reporting limit; reported as 0) (period starting 2022-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
A PFAS detection is not a violation. Federal limits (4 ppt for PFOA and PFOS) apply to running annual averages, with compliance required by 2029. In May 2026 EPA proposed extending the PFOA/PFOS deadline to 2031 and removing other PFAS limits; not final as of 2026-10-21.
Test your own tap
These are public records for whole systems. Your home's pipes, fixtures and any private well can change what you drink. A certified lab test or a hardness test strip gives you your own numbers. Then use our PFAS and lead filter selector to see which certifications to look for.
Common questions about Santa Clara County water
Is tap water in Santa Clara County safe to drink?
1 of the 6 largest systems here have at least one health-based violation in EPA records since October 2021 (see each system below for status). San Jose Water's most recent lead 90th percentile was below the lab detection limit (2023), below the 15 ppb action level. Public records can't guarantee what comes out of your tap, especially with older plumbing, so a home test is the surest check.
How hard is the water in Santa Clara County?
San Jose Water reports hardness from 77 to 451 mg/L depending on where you live, with no single system-wide average, so check your area in its report or test your water. For a 3-person home at 16.8 gpg (the harder plant's figure, since your address may get either), our softener calculator suggests a 24,000 grain unit as a starting point.
Is there PFAS in Santa Clara County water?
2 of the 6 sampled systems listed here detected at least one PFAS in EPA's UCMR 5 testing, and 2 results were above the level of a federal limit in at least one sample. A detection isn't a violation: federal PFAS limits apply to running annual averages starting in 2029.
Which water system serves my address in Santa Clara County?
Most homes are served by San Jose Water or one of the other systems listed on this page, but service areas don't follow county lines. Your water bill names your provider, and its annual Consumer Confidence Report has the full test results.
Data as of October 21, 2026. Figures are copied from public records and combined with our own calculations; they can be out of date or wrong. Tapped Out isn't affiliated with any utility or the EPA. Written and reviewed by the Tapped Out team. How we calculate · All sources.