Stanislaus County tap water: hardness, PFAS and lead

Stanislaus County, California has about 556,972 residents (Census 2024 estimate) and 61 community water systems in EPA records. The largest local system is Modesto, City of, serving about 218,915 people from surface water.

! 3 of 6 largest systems with health-based violationsPFAS detected at 2 of 6 sampled systemsHardness 13.4 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 Stanislaus County water?

Modesto, City of Estimate: untreated local water, not your tap · Low confidence

13.4 gpg (230 mg/L), very hard

Stanislaus County: median of 3,252 results from 542 monitoring sites (streams and wells). Utilities may blend or treat water, so your tap can differ.

Source: Hard Water Map county data, samples through 2021

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 13.4 gpg

For a 3-person home using 57 gallons per person per day and regenerating weekly, you'd remove about 16,040 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.

Open the softener calculator with 13.4 gpg

Largest water systems in Stanislaus County

The 6 biggest of 61 community water systems on EPA records for this county. Service areas don't follow county lines; your water bill names your provider.

Modesto, City of

CA5010010 · serves about 218,915 people · Surface water

✓ No health-based violations✓ Lead below action levelPFAS detected (7 types)

Lead 90th percentile: 12 ppb (period starting 2025-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).

  • PFOS: highest sample 26 ppt (15 of 86 samples); federal limit 4.0 ppt as a running annual average
  • PFHxS: highest sample 9.3 ppt (13 of 86 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)
  • PFOA: highest sample 8.6 ppt (8 of 86 samples); federal limit 4.0 ppt as a running annual average
  • PFPeA: highest sample 6.7 ppt (8 of 86 samples); no federal limit
  • PFHxA: highest sample 6.1 ppt (8 of 86 samples); no federal limit
  • PFBS: highest sample 4.3 ppt (2 of 86 samples); no individual limit; counted in EPA's PFAS mixture (hazard index) limit
  • PFHpA: highest sample 3.6 ppt (1 of 86 samples); no federal limit

EPA ECHO record

Turlock, City of

CA5010019 · serves about 72,888 people · Surface water

✓ No health-based violations✓ Lead below action level✓ No PFAS detected

Lead 90th percentile: 1 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).

EPA ECHO record

Ceres, City of

CA5010028 · serves about 54,513 people · Surface water

! 1 health-based violation✓ Lead below detectionPFAS detected (7 types)

Lead 90th percentile: <DL (below the lab detection/reporting limit; reported as 0) (period starting 2021-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).

  • PFOS: highest sample 24 ppt (2 of 16 samples); federal limit 4.0 ppt as a running annual average
  • PFOA: highest sample 12 ppt (2 of 16 samples); federal limit 4.0 ppt as a running annual average
  • PFPeA: highest sample 8.4 ppt (2 of 16 samples); no federal limit
  • PFHxA: highest sample 7.4 ppt (2 of 16 samples); no federal limit
  • PFBS: highest sample 6.6 ppt (2 of 16 samples); no individual limit; counted in EPA's PFAS mixture (hazard index) limit
  • PFHxS: highest sample 5.7 ppt (5 of 16 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)
  • PFHpA: highest sample 4.7 ppt (1 of 16 samples); no federal limit

EPA ECHO record

Riverbank, City of

CA5010018 · serves about 25,625 people · Groundwater

! 1 health-based violation! Lead above action level✓ No PFAS detected

Lead 90th percentile: 21 ppb (period starting 2024-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).

EPA ECHO record

Patterson, City of

CA5010017 · serves about 24,977 people · Groundwater

✓ 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).

EPA ECHO record

Oakdale, City of

CA5010014 · serves about 23,235 people · Groundwater

! 1 health-based violation✓ 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).

EPA ECHO record

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 Stanislaus County water

Is tap water in Stanislaus County safe to drink?

3 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). Modesto, City of's most recent lead 90th percentile was 12 ppb (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 Stanislaus County?

There's no published utility figure in our data, but untreated local stream and well samples in Stanislaus County have a median of about 13.4 grains per gallon (230 mg/L, very 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 13.4 gpg, our softener calculator suggests a 24,000 grain unit as a starting point.

Is there PFAS in Stanislaus County water?

2 of the 6 sampled systems listed here detected at least one PFAS in EPA's UCMR 5 testing, and 4 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 Stanislaus County?

Most homes are served by Modesto, City of 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.

More California counties

Sources for this page

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.