Nitrate is widespread in Tulare County wells.

1 widespread, 3 worth checking, 3 rare out of 7 health checks.

From 120 wells tested in Tulare County since 2002; your own well needs its own test. How to read this

Tested wells over the limit TulareCalifornia

Nitrate37%44 of 120 Uranium14%17 of 119 Arsenic10%12 of 120 Radon7%1 of 14 Manganese2%2 of 120 Fluoride0%0 of 119 Lead0%0 of 59

GermsTest every year, whatever the chart says

Coliform bacteria29%25 of 85 E. coli1%1 of 85

StainsNot a health risk

Iron stains2%3 of 120

Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+

Lab results: Water Quality Portal (USGS and EPA)

Show bacteria and iron

Who drinks from a well here

1 in 5 people 89,473 people

Nobody else tests these wells. Only you do.

People on wells: EPA researchers' 2020 estimate

How deep wells go here

Deep wells: fewer surface germs, more minerals from the rock.

Well depths: US Groundwater Well Database

Radon risk (a gas from rock)

LowMiddleHigh

Possible here. A home air test is inexpensive.

Radon zones: EPA map

Here's how Tulare County compares with California and the counties around it.

Each result puts Tulare County next to the 4 counties that border it, on the chart's 0 to 50% scale.

This one is widespread in Tulare County wells.

Nitrate44 of 120 wells over

About 4 in 10 wells tested here from 2002 to 2023 were over the EPA limit of 10 mg/L, against about 1 in 10 across California. Half the results were under 7.0 mg/L, and the top 1 in 10 were 20 mg/L or more. That's the highest share among the 47 California counties with 10 or more tested wells.

Tulare and its neighbors

Tulare37%

Fresno29%

Kern7%

Kings3%

Inyo0%

Nitrate guide

These 3 are worth checking in Tulare County.

Uranium17 of 119 wells over

About 1 in 7 wells tested here from 2002 to 2023 were over the EPA limit of 30 µg/L, against about 1 in 13 across California. Half the results were under 7.2 µg/L, and the top 1 in 10 were 36 µg/L or more. That's a bigger share than in 36 of the 43 other California counties with 10 or more tested wells.

Tulare and its neighbors

Fresno25%

Kings21%

Inyo17%

Tulare14%

Kern12%

Uranium guide

Arsenic12 of 120 wells over

About 1 in 10 wells tested here from 2002 to 2023 were over the EPA limit of 10 µg/L, against about 1 in 7 across California. Half the results were under 1.8 µg/L, and the top 1 in 10 were 6.7 µg/L or more. That's a bigger share than in 29 of the 46 other California counties with 10 or more tested wells.

Tulare and its neighbors

Kings45%

Kern25%

Inyo17%

Tulare10%

Fresno7%

Arsenic guide

Radon in water1 of 14 wells over

1 of 14 wells tested here from 2002 to 2014 was over 4,000 pCi/L, a level the EPA proposed, against about 1 in 30 across California. Half the results were under 620 pCi/L, and the top 1 in 10 were 2,240 pCi/L or more. That's a bigger share than in 25 of the 28 other California counties with 10 or more tested wells, leaving out 1 county whose results are likely overstated.

Tulare and its neighbors

Tulare7%

Kern2%

Fresno2%

Too few tested to show: Inyo, Kings.

Radon guide

These 3 are rare in Tulare County.

Manganese2 of 120 wells over

2 of 120 wells tested here from 2002 to 2023 were over the EPA health advisory of 0.3 mg/L, against about 1 in 12 across California. At least half the results were too low for the lab to measure, and the top 1 in 10 were 0.0044 mg/L or more. That's a smaller share than in 39 of the 45 other California counties with 10 or more tested wells.

Tulare and its neighbors

Kings12%

Kern10%

Fresno7%

Tulare2%

Inyo0%

Manganese guide

Fluoride0 of 119 wells over

None of the 119 wells tested here from 2002 to 2023 were over the EPA limit of 4 mg/L, against about 1 in 37 across California. Half the results were under 0.12 mg/L, and the top 1 in 10 were 0.27 mg/L or more. Tulare County had none, while 11 of the 44 other California counties with 10 or more tested wells had at least one.

Tulare and its neighbors

Inyo4%

Fresno0%

Kern0%

Kings0%

Tulare0%

Lead0 of 59 wells over

None of the 59 wells tested here from 2002 to 2023 were over the EPA action level of 15 µg/L, against under 1 in 100 across California. At least half the results were too low for the lab to measure, and the top 1 in 10 were 1.7 µg/L or more. Tulare County had none, while 5 of the 42 other California counties with 10 or more tested wells had at least one.

Tulare and its neighbors

Fresno0%

Inyo0%

Kern0%

Kings0%

Tulare0%

Lead guide

Coliform bacteria turned up in 25 of 85 tested Tulare County wells, so test for it every year.

Coliform bacteria25 of 85 wells had it

About 3 in 10 wells tested here from 2002 to 2015 had coliform bacteria, against about 2 in 10 across California.

Tulare and its neighbors

Fresno40%

Tulare29%

Kings28%

Kern11%

Too few tested to show: Inyo.

Bacteria guide

E. coli1 of 85 wells had it

1 of 85 wells tested here from 2002 to 2015 had E. coli, against about 1 in 23 across California.

Tulare and its neighbors

Kern2%

Fresno2%

Tulare1%

Kings0%

Too few tested to show: Inyo.

E. coli means human or animal waste is getting in, so if a test of your Tulare County well finds it, boil drinking water until the well is fixed.

Bacteria guide

Iron reached staining levels in 3 of 120 tested wells, and it isn't a health risk.

Iron stains3 of 120 wells had it

3 of 120 wells tested here from 2002 to 2023 had enough iron to stain (0.3 mg/L), against about 1 in 10 across California.

Tulare and its neighbors

Kings15%

Kern10%

Inyo8%

Fresno4%

Tulare2%

Iron guide

Tulare County has 120 tested wells, and the busiest decade for testing was the 2010s.

35 wells had a test in the 2000s, 98 in the 2010s and 21 since 2020.

Only 21 of the 120 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.

Most Tulare County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).

One mail-in lab test covers the 5 things to check in Tulare County.

Bacteria
Nitrate
Uranium
Arsenic
Radon in water

What California offers well owners

Free testingThe State and Regional Water Boards fund or regulate 11 domestic well programs that offer free well testing in their service areas. See the program
Certified labsCalifornia's list of certified labs
Well recordsCalifornia's well record search

Half the household wells here are shallower than 200 feet.

That comes from 9,903 household wells in California's drilling records. Most wells of every kind here are 155 to 400 feet deep. Wells as deep as Tulare County's are usually better protected from fertilizer and bacteria at the surface, but they can pick up more of what's in the rock, like arsenic and uranium. Typical household wells here are shallower than in 27 of the 56 other California counties with enough drilling records.

Look up your own well's depth in California's well record search, or see how to find it.

Well depths: US Groundwater Well Database

Here's what we know about radon and PFAS in Tulare County.

Tulare County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide

Between 2023 and 2025 the EPA had 16 town water systems in Tulare County test for PFAS. 3 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 23 ng/L of PFOS. Only 23 wells in Tulare County have public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide

Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025

Next door to Tulare County

Fresno Kern

Elsewhere in California

Riverside Los Angeles Sonoma San Diego San Bernardino Placer

All of California

Questions people ask about well water in Tulare County

Is well water in Tulare County safe to drink?

44 of 120 wells tested in Tulare County had nitrate over the limit, about 4 in 10. Across California it's about 1 in 10. That's the highest share among the 47 California counties with 10 or more tested wells. So test your own well for nitrate before you count on it.

Can I get my well tested for free in Tulare County?

The State and Regional Water Boards fund or regulate 11 domestic well programs that offer free well testing in their service areas. If not, use a lab California has certified for drinking water. Ask for bacteria, nitrate, uranium, arsenic and radon in water, the tests that matter most in Tulare County.

How deep are wells in Tulare County?

Half the household wells here are shallower than 200 feet. Typical household wells here are shallower than in 27 of the 56 other California counties with enough drilling records.

How does Tulare County compare with the counties around it?

For nitrate, the share of tested wells over the limit: Tulare County, at 37%, had a higher share than all 4 neighboring counties with data. Groundwater doesn't stop at county lines, so Fresno's 29% is worth knowing about if you live near it.

How often should I test my well in Tulare County?

In Tulare County, 25 of 85 tested wells had coliform bacteria, so the CDC's advice matters here: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.

By the Tested Water teamData from the USGS, EPA and State Water Resources Control BoardUpdated November 8, 2026

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Where the Tulare County numbers come from

People on wells: 89,473 in Tulare County, from EPA estimates built on the 2020 Census (Murray et al.).
Lab tests: 1,342 well water samples from 120 wells in the Water Quality Portal, run by the USGS and EPA, 2002 to 2023.
Well depths: 9,903 California drilling records for Tulare County, gathered in the US Groundwater Well Database (Lin and others, 2024).
Neighboring counties: the 4 counties that share a border with Tulare County, from the Census Bureau's county adjacency file.
PFAS: EPA tests of 16 town water systems in Tulare County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
Radon: Tulare County is zone 2 on the EPA Map of Radon Zones.
State programs and links: State Water Resources Control Board, checked November 1, 2026.

Download this county's data (CSV)How we read these numbers Report an error