San Joaquin County tap water: hardness, PFAS and lead
San Joaquin County, California has about 816,108 residents (Census 2024 estimate) and 93 community water systems in EPA records. The largest local system is City of Stockton, serving about 192,702 people from surface water.
! 1 of 6 largest systems with health-based violationsPFAS detected at 5 of 6 sampled systemsHardness 7.6 gpg (low confidence)
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 San Joaquin County water?
City of StocktonEstimate: untreated local water, not your tap · Low confidence
7.6 gpg(130 mg/L), hard
San Joaquin County: median of 3,662 results from 599 monitoring sites (streams and wells). Utilities may blend or treat water, so your tap can differ.
County estimates: Hard Water Map (hardwatermap.com), CC BY 4.0, derived from the USGS/EPA Water Quality Portal; file generated 2026-07-22. License
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 7.6 gpg
For a 3-person home using 57 gallons per person per day and regenerating weekly, you'd remove about 9,097 grains between regenerations. Suggested size: 24,000 grain. This uses a low-confidence county estimate, so confirm with a test first.
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 93 community water systems on EPA records for this county. Service areas don't follow county lines; your water bill names your provider.
City of Stockton
CA3910012 · serves about 192,702 people · Surface water
! 2 health-based violations✓ Lead below detectionPFAS detected (3 types)
Lead 90th percentile: <DL (below the lab detection/reporting limit; reported as 0) (period starting 2025-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
PFOS: highest sample 28 ppt (3 of 38 samples); federal limit 4.0 ppt as a running annual average
PFOA: highest sample 6.7 ppt (1 of 38 samples); federal limit 4.0 ppt as a running annual average
PFBS: highest sample 6.2 ppt (1 of 38 samples); no individual limit; counted in EPA's PFAS mixture (hazard index) limit
CA3910001 · serves about 182,775 people · Surface water
✓ No health-based violations✓ Lead below detectionPFAS detected (1 type)
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).
PFOS: highest sample 5.2 ppt (2 of 28 samples); federal limit 4.0 ppt as a running annual average
CA3910011 · serves about 98,215 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).
CA3910005 · serves about 84,928 people · Surface water
✓ No health-based violations✓ Lead below action levelPFAS detected (4 types)
Lead 90th percentile: 0.4 ppb (period starting 2022-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
PFHxS: highest sample 19 ppt (6 of 24 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)
PFHxA: highest sample 9.5 ppt (2 of 24 samples); no federal limit
PFOA: highest sample 7 ppt (4 of 24 samples); federal limit 4.0 ppt as a running annual average
PFBS: highest sample 3.9 ppt (2 of 24 samples); no individual limit; counted in EPA's PFAS mixture (hazard index) limit
CA3910004 · serves about 67,093 people · Surface water
✓ No health-based violations✓ Lead below detectionPFAS detected (7 types)
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).
PFBS: highest sample 17 ppt (5 of 50 samples); no individual limit; counted in EPA's PFAS mixture (hazard index) limit
PFOA: highest sample 6.2 ppt (2 of 50 samples); federal limit 4.0 ppt as a running annual average
PFHxS: highest sample 6.1 ppt (4 of 50 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)
PFOS: highest sample 5.6 ppt (2 of 50 samples); federal limit 4.0 ppt as a running annual average
PFPeA: highest sample 5.4 ppt (4 of 50 samples); no federal limit
PFHxA: highest sample 5 ppt (4 of 50 samples); no federal limit
PFHpA: highest sample 3.3 ppt (1 of 50 samples); no federal limit
CA3910015 · serves about 38,596 people · Surface water
✓ No health-based violations✓ Lead below detectionPFAS detected (3 types)
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).
PFOS: highest sample 17 ppt (2 of 6 samples); federal limit 4.0 ppt as a running annual average
PFBS: highest sample 5 ppt (2 of 6 samples); no individual limit; counted in EPA's PFAS mixture (hazard index) limit
PFHxS: highest sample 3.5 ppt (1 of 6 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)
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 San Joaquin County water
Is tap water in San Joaquin 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). City of Stockton's most recent lead 90th percentile was below the lab detection limit (2025), 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 San Joaquin County?
There's no published utility figure in our data, but untreated local stream and well samples in San Joaquin County have a median of about 7.6 grains per gallon (130 mg/L, hard). That's a low-confidence estimate of source water, not your tap, so test before you buy equipment. For a 3-person home at 7.6 gpg, our softener calculator suggests a 24,000 grain unit as a starting point.
Is there PFAS in San Joaquin County water?
5 of the 6 sampled systems listed here detected at least one PFAS in EPA's UCMR 5 testing, and 8 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 San Joaquin County?
Most homes are served by City of Stockton 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.