Health problems are rare in tested Harris County wells.

All 7 health checks came back rare here.

From 164 wells tested in Harris County since 2000; your own well needs its own test. How to read this

Tested wells over the limit HarrisTexas

Nitrate5%2 of 42 Manganese3%4 of 148 Arsenic2%4 of 162 Uranium2%3 of 162 Fluoride0%0 of 163 Radon0%0 of 63 Lead0%0 of 64

GermsTest every year, whatever the chart says

Coliform bacteria30%3 of 10 E. coli0%0 of 10

StainsNot a health risk

Iron stains7%11 of 162

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

About 1 in 16 people 298,130 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

Less likely, but the EPA still says test your air.

Radon zones: EPA map

Here's how Harris County compares with Texas and the counties around it.

Each result puts Harris County next to the 7 counties that border it, on the chart's 0 to 50% scale.

All 7 health checks are rare in Harris County.

Nitrate2 of 42 wells over

2 of 42 wells tested here from 2000 to 2015 were over the EPA limit of 10 mg/L, against about 1 in 21 across Texas. Half the results were under 0.25 mg/L, and the top 1 in 10 were 3.5 mg/L or more. That's a bigger share than in 17 of the 22 other Texas counties with 10 or more tested wells.

Harris and its neighbors

Harris5%

Montgomery0%

Too few tested to show: Brazoria, Chambers, Fort Bend, Galveston, Liberty, Waller.

Nitrate guide

Manganese4 of 148 wells over

About 1 in 37 wells tested here from 2002 to 2016 were over the EPA health advisory of 0.3 mg/L, against about 1 in 45 across Texas. Half the results were under 0.0076 mg/L, and the top 1 in 10 were 0.064 mg/L or more. That's a bigger share than in 12 of the 17 other Texas counties with 10 or more tested wells, leaving out 1 county whose results are likely overstated.

Harris and its neighbors

Harris3%

Brazoria0%

Montgomery0%

Too few tested to show: Chambers, Fort Bend, Galveston, Liberty, Waller.

Manganese guide

Arsenic4 of 162 wells over

About 1 in 40 wells tested here from 2002 to 2016 were over the EPA limit of 10 µg/L, against about 1 in 10 across Texas. Half the results were under 2.3 µg/L, and the top 1 in 10 were 4.7 µg/L or more. That's a bigger share than in 10 of the 16 other Texas counties with 10 or more tested wells, leaving out 1 county whose results are likely overstated.

Harris and its neighbors

Montgomery5%

Harris2%

Too few tested to show: Brazoria, Chambers, Fort Bend, Galveston, Liberty, Waller.

Arsenic guide

Uranium3 of 162 wells over

3 of 162 wells tested here from 2002 to 2016 were over the EPA limit of 30 µg/L, against under 1 in 100 across Texas. Half the results were under 1.5 µg/L, and the top 1 in 10 were 9.9 µg/L or more. That's a bigger share than in 15 of the 17 other Texas counties with 10 or more tested wells.

Harris and its neighbors

Harris2%

Montgomery0%

Too few tested to show: Brazoria, Chambers, Fort Bend, Galveston, Liberty, Waller.

Uranium guide

Fluoride0 of 163 wells over

None of the 163 wells tested here from 2002 to 2016 were over the EPA limit of 4 mg/L, against about 1 in 23 across Texas. Half the results were under 0.22 mg/L, and the top 1 in 10 were 0.65 mg/L or more. Harris County had none, while 5 of the 19 other Texas counties with 10 or more tested wells had at least one.

Harris and its neighbors

Brazoria0%

Harris0%

Montgomery0%

Too few tested to show: Chambers, Fort Bend, Galveston, Liberty, Waller.

Radon in water0 of 63 wells over

None of the 63 wells tested here from 2002 to 2016 were over 4,000 pCi/L, a level the EPA proposed, against under 1 in 100 across Texas. Half the results were under 580 pCi/L, and the top 1 in 10 were 1,670 pCi/L or more. Harris County had none, and neither did any of the 3 other Texas counties with 10 or more tested wells.

Harris and its neighbors

Harris0%

Montgomery0%

Too few tested to show: Brazoria, Chambers, Fort Bend, Galveston, Liberty, Waller.

Radon guide

Lead0 of 64 wells over

None of the 64 wells tested here from 2002 to 2015 were over the EPA action level of 15 µg/L, against under 1 in 100 across Texas. At least half the results were too low for the lab to measure, and the top 1 in 10 were 0.59 µg/L or more. Harris County had none, and neither did any of the 17 other Texas counties with 10 or more tested wells.

Harris and its neighbors

Harris0%

Montgomery0%

Too few tested to show: Brazoria, Chambers, Fort Bend, Galveston, Liberty, Waller.

Lead guide

Coliform bacteria turned up in 3 of 10 tested Harris County wells, so test for it every year.

Coliform bacteria3 of 10 wells had it

3 of 10 wells tested here from 2002 to 2014 had coliform bacteria, against about 3 in 10 across Texas.

Bacteria guide

E. coli0 of 10 wells had it

None of the 10 wells tested here from 2002 to 2014 had E. coli, against about 1 in 13 across Texas.

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

Bacteria guide

Iron reached staining levels in 11 of 162 tested wells, and it isn't a health risk.

Iron stains11 of 162 wells had it

About 1 in 15 wells tested here from 2002 to 2016 had enough iron to stain (0.3 mg/L), against about 1 in 9 across Texas.

Harris and its neighbors

Brazoria55%

Montgomery8%

Harris7%

Too few tested to show: Chambers, Fort Bend, Galveston, Liberty, Waller.

Iron guide

Harris County has 164 tested wells, and the busiest decade for testing was the 2010s.

58 wells had a test in the 2000s and 152 in the 2010s.

None of the 164 wells has a test from 2020 or later, so a fresh test of your own well tells you more than any of these.

Most Harris 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 3 things to check in Harris County.

Bacteria
Nitrate
Arsenic

What Texas offers well owners

Free testingTexas A&M AgriLife Extension's Texas Well Owner Network holds periodic county well water screenings, some free and some for a small per-sample fee. See the program
Certified labsTexas's list of certified labs
Well recordsTexas's well record search

Half the household wells here are shallower than 265 feet.

That comes from 7,772 household wells in Texas's drilling records. Most wells of every kind here are 28 to 338 feet deep. Wells as deep as Harris 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 go deeper than in 129 of the 248 other Texas counties with enough drilling records.

Look up your own well's depth in Texas'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 Harris County.

Harris County is in the EPA's lowest radon zone, so radon from well water is unlikely to be a problem. Radon guide

Between 2023 and 2025 the EPA had 261 town water systems in Harris County test for PFAS. 12 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 9.7 ng/L of PFOS. No well in Harris County has 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 Harris County

Montgomery Brazoria

Elsewhere in Texas

Tarrant Travis

All of Texas

Questions people ask about well water in Harris County

Is well water in Harris County safe to drink?

Most tested wells in Harris County came in under the limits. Of 7 health checks with enough tests, nitrate came closest, at 2 of 42 wells over. Every well is different, so test yours for bacteria, nitrate and arsenic.

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

Texas A&M AgriLife Extension's Texas Well Owner Network holds periodic county well water screenings, some free and some for a small per-sample fee. If not, use a lab Texas has certified for drinking water. Ask for bacteria, nitrate and arsenic, the tests that matter most in Harris County.

How deep are wells in Harris County?

Half the household wells here are shallower than 265 feet. Typical household wells here go deeper than in 129 of the 248 other Texas counties with enough drilling records.

How does Harris County compare with the counties around it?

For nitrate, the share of tested wells over the limit: Montgomery, the one neighbor with data, came in lower than Harris County, at 0% against 5%. Groundwater doesn't stop at county lines, so Montgomery's 0% is worth knowing about if you live near it.

How often should I test my well in Harris County?

In Harris County, 3 of 10 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 Texas Water Development Board and Texas Commission on Environmental Quality (TCEQ)Updated November 8, 2026

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Where the Harris County numbers come from

People on wells: 298,130 in Harris County, from EPA estimates built on the 2020 Census (Murray et al.).
Lab tests: 1,680 well water samples from 164 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2016.
Well depths: 7,772 Texas drilling records for Harris County, gathered in the US Groundwater Well Database (Lin and others, 2024).
Neighboring counties: the 7 counties that share a border with Harris County, from the Census Bureau's county adjacency file.
PFAS: EPA tests of 261 town water systems in Harris County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
Radon: Harris County is zone 3 on the EPA Map of Radon Zones.
State programs and links: Texas Water Development Board and Texas Commission on Environmental Quality (TCEQ), checked November 1, 2026.

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