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Nitrate in Oklahoma well water, by county

By the Tested Water teamLab data from the USGS and EPA Water Quality Portal, 2000 to 2021Updated November 8, 2026

Nitrate is widespread, over the limit in 15% or more of tested wells, in 17 of the 40 Oklahoma 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 Oklahoma compares with the rest of the country

Across Oklahoma, about 1 in 8 tested wells had nitrate over the EPA limit of 10 mg/L (242 of 1,830). Across all tested wells in the US it's about 1 in 12. So nitrate turns up somewhat more often in Oklahoma than in the country as a whole. Check your county 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
Greer County 12
42% 5 of 12
 Widespread
Garfield County 26
31% 8 of 26
 Widespread
Kingfisher County 119
30% 36 of 119
 Widespread
Harper County 37
30% 11 of 37
 Widespread
Washita County 24
25% 6 of 24
 Widespread
Blaine County 37
24% 9 of 37
 Widespread
Logan County 21
24% 5 of 21
 Widespread
Major County 148
23% 34 of 148
 Widespread
Texas County 110
22% 24 of 110
 Widespread
Grady County 14
21% 3 of 14
 Widespread
Caddo County 59
20% 12 of 59
 Widespread
Woods County 30
20% 6 of 30
 Widespread
Pontotoc County 25
20% 5 of 25
 Widespread
Alfalfa County 16
19% 3 of 16
 Widespread
Pawnee County 16
19% 3 of 16
 Widespread
Ellis County 28
18% 5 of 28
 Widespread
Beaver County 73
16% 12 of 73
 Widespread
Canadian County 27
15% 4 of 27
 Worth checking
Osage County 44
14% 6 of 44
 Worth checking
Hughes County 39
13% 5 of 39
 Worth checking
McCurtain County 18
11% 2 of 18
 Worth checking
Custer County 20
10% 2 of 20
 Worth checking
Payne County 10
10% 1 of 10
 Worth checking
Murray County 12
8% 1 of 12
 Worth checking
Woodward County 161
6% 10 of 161
 Worth checking
Lincoln County 17
6% 1 of 17
 Worth checking
Beckham County 26
4% 1 of 26
 Rare
Johnston County 26
4% 1 of 26
 Rare
Pottawatomie County 53
4% 2 of 53
 Rare
Oklahoma County 157
1% 1 of 157
 Rare
Cleveland County 158
0% 0 of 158
 Rare
Seminole County 25
0% 0 of 25
 Rare
Stephens County 16
0% 0 of 16
 Rare
Ottawa County 15
0% 0 of 15
 Rare
Bryan County 14
0% 0 of 14
 Rare
Kay County 13
0% 0 of 13
 Rare
Marshall County 12
0% 0 of 12
 Rare
Comanche County 11
0% 0 of 11
 Rare
Cimarron County 10
0% 0 of 10
 Rare
Delaware County 10
0% 0 of 10
 Rare

33 more Oklahoma 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 Oklahoma

1

Your county health department

Oklahoma doesn't run a statewide free testing program that we know of. Some county health departments test wells or sell kits, so call yours first.

Oklahoma's private well page
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 Oklahoma

Questions people ask about nitrate in Oklahoma

Is there nitrate in Oklahoma well water?

Nitrate is widespread, over the limit in 15% or more of tested wells, in 17 of the 40 Oklahoma counties with 10 or more tested wells. Across Oklahoma, about 1 in 8 tested wells had nitrate over the EPA limit of 10 mg/L (242 of 1,830). Across all tested wells in the US it's about 1 in 12. So nitrate turns up somewhat more often in Oklahoma than in the country as a whole. Check your county below.

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

Use a lab certified by Oklahoma for drinking water, or a mail-in kit that includes nitrate from a certified lab. Some county health departments test wells too, so call yours first.

See Oklahoma'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: Department of Environmental Quality.