Idaho well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Idaho county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 44 counties
- Canyon CountyWell users 34,600Arsenic about 34 in 100Nitrate 3.3 mg/L
- Ada CountyWell users 30,600Arsenic about 17 in 100Nitrate 2.7 mg/L
- Bingham CountyWell users 20,600Arsenic about 7 in 100Nitrate 3.1 mg/L
- Twin Falls CountyWell users 19,300Arsenic about 50 in 100Nitrate 7.3 mg/L
- Bonner CountyWell users 16,200Arsenic about 8 in 100Nitrate 0.1 mg/L
- Bonneville CountyWell users 12,500Arsenic about 7 in 100Nitrate 2.9 mg/L
- Jefferson CountyWell users 12,200Arsenic about 12 in 100Nitrate 3.4 mg/L
- Kootenai CountyWell users 12,100Arsenic about 11 in 100Nitrate 0.3 mg/L
- Madison CountyWell users 10,100Arsenic about 9 in 100Nitrate 2.7 mg/L
- Minidoka CountyWell users 9,900Arsenic about 7 in 100Nitrate 4.0 mg/L
- Cassia CountyWell users 9,800Arsenic about 10 in 100Nitrate 4.6 mg/L
- Jerome CountyWell users 9,000Arsenic about 8 in 100Nitrate 3.4 mg/L
- Payette CountyWell users 8,200Arsenic about 36 in 100Nitrate 0.7 mg/L
- Elmore CountyWell users 8,200Arsenic about 16 in 100Nitrate 1.3 mg/L
- Bannock CountyWell users 7,900Arsenic about 8 in 100Nitrate 2.0 mg/L
- Gem CountyWell users 7,500Arsenic about 25 in 100Nitrate 1.3 mg/L
- Latah CountyWell users 7,300Arsenic about 7 in 100Nitrate 0.1 mg/L
- Gooding CountyWell users 6,500Arsenic about 17 in 100Nitrate 3.7 mg/L
- Idaho CountyWell users 6,000Arsenic about 5 in 100Nitrate 0.1 mg/L
- Fremont CountyWell users 5,800Arsenic about 9 in 100Nitrate 2.0 mg/L
- Owyhee CountyWell users 5,600Arsenic about 45 in 100Nitrate 0.9 mg/L
- Blaine CountyWell users 5,500Arsenic about 5 in 100Nitrate 0.4 mg/L
- Valley CountyWell users 5,400Arsenic about 5 in 100Nitrate 0.1 mg/L
- Teton CountyWell users 5,300Arsenic about 5 in 100Nitrate 1.0 mg/L
- Lemhi CountyWell users 4,400Arsenic about 7 in 100Nitrate 0.3 mg/L
- Nez Perce CountyWell users 3,400Arsenic about 6 in 100Nitrate 0.1 mg/L
- Washington CountyWell users 3,300Arsenic about 17 in 100Nitrate 0.5 mg/L
- Boise CountyWell users 2,700Arsenic about 5 in 100Nitrate 0.1 mg/L
- Power CountyWell users 2,500Arsenic about 7 in 100Nitrate 1.1 mg/L
- Benewah CountyWell users 2,400Arsenic about 10 in 100Nitrate 0.0 mg/L
- Boundary CountyWell users 2,100Arsenic about 8 in 100Nitrate 0.1 mg/L
- Clearwater CountyWell users 2,100Arsenic about 5 in 100Nitrate 0.0 mg/L
- Lincoln CountyWell users 2,100Arsenic about 6 in 100Nitrate 1.1 mg/L
- Custer CountyWell users 1,900Arsenic about 4 in 100Nitrate 0.2 mg/L
- Oneida CountyWell users 1,800Arsenic about 5 in 100Nitrate 0.9 mg/L
- Adams CountyWell users 1,800Arsenic about 5 in 100Nitrate 0.1 mg/L
- Franklin CountyWell users 1,700Arsenic about 12 in 100Nitrate 0.9 mg/L
- Caribou CountyWell users 1,500Arsenic about 7 in 100Nitrate 0.4 mg/L
- Butte CountyWell users 1,400Arsenic about 10 in 100Nitrate 0.6 mg/L
- Shoshone CountyWell users 1,200Arsenic about 7 in 100Nitrate 0.0 mg/L
- Bear Lake CountyWell users 1,200Arsenic about 6 in 100Nitrate 0.2 mg/L
- Lewis CountyWell users 680Arsenic about 5 in 100Nitrate 0.2 mg/L
- Camas CountyWell users 640Arsenic about 9 in 100Nitrate 0.3 mg/L
- Clark CountyWell users 310Arsenic about 7 in 100Nitrate 0.2 mg/L
Each mark = 1 in 100 well users the model places above 10 µg/L arsenic (scale 0–10)10 mg/L nitrate: the federal limit (MCL) for public systems
- These figures describe the area, not your well. Only a lab test shows what’s in your water.
- CDC says the Well Water Index figures “do not describe risk to individual wells.” (CDC Tracking Network)
- The arsenic model is better at spotting low-arsenic areas than at confirming high ones.
- Well-user counts are 2010 USGS estimates; tract values are averages over each census tract.
- Total coliform bacteriaEvery year
- NitrateEvery year
- Total dissolved solidsEvery year
- pHEvery year
- ArsenicAsk your local health department
EPA: Private Drinking Water Wells · CDC: Guidelines for Testing Well Water
Use a state-certified lab
Idaho Department of Health & Welfare lists the laboratories certified to test drinking water in Idaho.
Screening tells you if something is worth a closer look
A lab result is the number you can act on.
As an Amazon Associate, PurityMap earns from qualifying purchases. Affiliate disclosure
Lab-certified results
ETR Labs Basic Water Quality Test Kit
ETR Laboratories
50+ substances, including lead, copper, arsenic, nitrate, hardness and coliform bacteria
- Analyzed by Environmental Testing and Research Laboratories (ETR Labs), Leominster, MA · ISO/IEC 17025:2017, ANAB certificate AT-2638
- Turnaround: 2–4 business days after the lab receives it
What it can't tell you: It does not test PFAS, and not every result on the panel falls under the lab's accredited scope.
Screening: quick check, not lab-grade
Watersafe Drinking Water Test Kit
Silver Lake Research
Lead, bacteria, nitrate, copper, iron, chlorine, hardness and pH
- Turnaround: Minutes; the bacteria test can take up to 48 hours
What it can't tell you: Each test gives a yes/no or a rough range, not a lab number, and it cannot detect PFAS or arsenic.
A mail-in kit’s lab is accredited (ISO/IEC 17025) but may not be certified by your state. For a home sale, a loan, or a health-department follow-up, use a state-certified lab.
Idaho well water
Sources: CDC Well Water Index (2024) · USGS arsenic and nitrate models · USGS domestic well populations · EPA and CDC testing guidance. Data last updated 2026-10-08. All sources →
How many people use private wells in Idaho?
About 315,200 people across 44 Idaho counties, by the USGS 2010 estimate. USGS models place about 51,800 of them in areas where wells are likely to be above the 10 µg/L arsenic limit. These are area estimates, not well results.
Are private wells regulated in Idaho?
The quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments and laws. (EPA) Testing and treatment are the owner's responsibility.
Where can I get my well tested in Idaho?
Idaho Department of Health & Welfare keeps the list of laboratories certified to test drinking water in Idaho. Only use laboratories that are certified to do drinking water testing. (EPA)