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Nitrate in Idaho well water, by county

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

Nitrate is widespread, over the limit in 15% or more of tested wells, in 2 of the 44 Idaho 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 Idaho compares with the rest of the country

Across Idaho, about 1 in 24 tested wells had nitrate over the EPA limit of 10 mg/L (121 of 2,859). 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
Washington County 36
25% 9 of 36
 Widespread
Lewis County 17
18% 3 of 17
 Widespread
Elmore County 122
12% 15 of 122
 Worth checking
Canyon County 169
11% 18 of 169
 Worth checking
Bingham County 90
9% 8 of 90
 Worth checking
Twin Falls County 125
9% 11 of 125
 Worth checking
Cassia County 60
8% 5 of 60
 Worth checking
Clearwater County 13
8% 1 of 13
 Worth checking
Franklin County 13
8% 1 of 13
 Worth checking
Nez Perce County 28
7% 2 of 28
 Worth checking
Owyhee County 57
7% 4 of 57
 Worth checking
Fremont County 43
7% 3 of 43
 Worth checking
Ada County 167
7% 11 of 167
 Worth checking
Boundary County 17
6% 1 of 17
 Worth checking
Kootenai County 52
6% 3 of 52
 Worth checking
Bear Lake County 22
5% 1 of 22
 Rare
Power County 49
4% 2 of 49
 Rare
Caribou County 113
4% 4 of 113
 Rare
Gooding County 58
3% 2 of 58
 Rare
Payette County 32
3% 1 of 32
 Rare
Jefferson County 67
3% 2 of 67
 Rare
Jerome County 109
2% 2 of 109
 Rare
Minidoka County 404
2% 7 of 404
 Rare
Teton County 60
2% 1 of 60
 Rare
Gem County 64
2% 1 of 64
 Rare
Butte County 229
1% 3 of 229
 Rare
Shoshone County 79
0% 0 of 79
 Rare
Blaine County 70
0% 0 of 70
 Rare
Bonner County 57
0% 0 of 57
 Rare
Bannock County 53
0% 0 of 53
 Rare
Lincoln County 44
0% 0 of 44
 Rare
Latah County 37
0% 0 of 37
 Rare
Benewah County 36
0% 0 of 36
 Rare
Idaho County 36
0% 0 of 36
 Rare
Bonneville County 34
0% 0 of 34
 Rare
Custer County 32
0% 0 of 32
 Rare
Clark County 29
0% 0 of 29
 Rare
Lemhi County 24
0% 0 of 24
 Rare
Madison County 23
0% 0 of 23
 Rare
Oneida County 22
0% 0 of 22
 Rare
Valley County 21
0% 0 of 21
 Rare
Boise County 20
0% 0 of 20
 Rare
Adams County 15
0% 0 of 15
 Rare
Camas County 11
0% 0 of 11
 Rare

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Where to get your well tested for nitrate in Idaho

1

Free state testing

Idaho sends well owners a free test kit, one per household every 5 years. Check which tests it includes before you count on it for nitrate.

Idaho's private well page
2

A lab Idaho certifies

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

Labs certified by Idaho
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 Idaho

Questions people ask about nitrate in Idaho

Is there nitrate in Idaho well water?

Nitrate is widespread, over the limit in 15% or more of tested wells, in 2 of the 44 Idaho counties with 10 or more tested wells. Across Idaho, about 1 in 24 tested wells had nitrate over the EPA limit of 10 mg/L (121 of 2,859). 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 Idaho?

Idaho sends well owners a free test kit, one per household every 5 years. If that doesn't cover you, use a lab certified by Idaho for drinking water, or a mail-in kit that includes nitrate from a certified lab.

See Idaho'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 Health and Welfare.