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Nitrate in Texas well water, by county

By the Tested Water teamLab data from the USGS and EPA Water Quality Portal, 2000 to 2023Updated November 8, 2026

Nitrate is widespread, over the limit in 15% or more of tested wells, in 3 of the 23 Texas counties with 10 or more tested wells. A county's share tells you how likely a problem is nearby. Only a test of your own well tells you what's in it.

Find a nitrate test See every county

How Texas compares with the rest of the country

Across Texas, about 1 in 21 tested wells had nitrate over the EPA limit of 10 mg/L (50 of 1,039). Across all tested wells in the US it's about 1 in 12. That's less often than in the country as a whole. Counties still differ, so check yours below.

Why it matters: It's dangerous for babies under 6 months, because it keeps their blood from carrying enough oxygen.

Nitrate soaks down into groundwater from fertilizer, manure and septic systems.

Nitrate in tested wells, county by county

Share of each county's tested wells with at least one result over the EPA limit of 10 mg/L. Counties need 10 or more tested wells to be listed. Widespread means 15% or more, worth checking 5 to 15%, rare under 5%.

CountyWells testedWells over the limitLevel
Terry County 22
55% 12 of 22
 Widespread
Lubbock County 10
30% 3 of 10
 Widespread
Gaines County 20
20% 4 of 20
 Widespread
Yoakum County 26
12% 3 of 26
 Worth checking
Lamb County 12
8% 1 of 12
 Worth checking
Harris County 42
5% 2 of 42
 Rare
Medina County 26
4% 1 of 26
 Rare
El Paso County 60
2% 1 of 60
 Rare
Bexar County 94
0% 0 of 94
 Rare
Pecos County 35
0% 0 of 35
 Rare
Tarrant County 35
0% 0 of 35
 Rare
Travis County 30
0% 0 of 30
 Rare
Hays County 29
0% 0 of 29
 Rare
Uvalde County 23
0% 0 of 23
 Rare
Comal County 22
0% 0 of 22
 Rare
Williamson County 22
0% 0 of 22
 Rare
Montgomery County 19
0% 0 of 19
 Rare
Burnet County 15
0% 0 of 15
 Rare
Wilson County 13
0% 0 of 13
 Rare
Hale County 12
0% 0 of 12
 Rare
Bell County 11
0% 0 of 11
 Rare
Goliad County 10
0% 0 of 10
 Rare
Panola County 10
0% 0 of 10
 Rare

156 more Texas counties have 1 to 9 tested wells for nitrate, too few to rate.

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Where to get your well tested for nitrate in Texas

1

Free testing, with limits

Texas A&M holds county well screenings around Texas, some free and some for a small fee. Check which tests it includes before you count on it for nitrate.

Texas's private well page
2

A lab Texas certifies

Ask for nitrate by name. Results from a certified lab count for a home sale or a loan.

Labs certified by Texas
3

A mail-in kit

Fill the bottles at your kitchen tap and mail them back. We mark the kits that include nitrate.

Compare kits

Keep reading about wells in Texas

Questions people ask about nitrate in Texas

Is there nitrate in Texas well water?

Nitrate is widespread, over the limit in 15% or more of tested wells, in 3 of the 23 Texas counties with 10 or more tested wells. Across Texas, about 1 in 21 tested wells had nitrate over the EPA limit of 10 mg/L (50 of 1,039). Across all tested wells in the US it's about 1 in 12. That's less often than in the country as a whole. Counties still differ, so check yours below.

Where can I get my well tested for nitrate in Texas?

Texas A&M holds county well screenings around Texas, some free and some for a small fee. If that doesn't cover you, use a lab certified by Texas for drinking water, or a mail-in kit that includes nitrate from a certified lab.

See Texas's list of certified labs, or compare mail-in kits.

Where these numbers come from

  • Lab tests: Water Quality Portal (USGS and EPA), well samples since 2000. A well counts as over if any of its tests was over the EPA limit of 10 mg/L. Wells tested for studies and monitoring, not a random sample of homes.
  • Likely overstated: our own check of who tested the wells, when and where. How we check.
  • State programs and links: Texas Water Development Board and Texas Commission on Environmental Quality (TCEQ).