Well water in Idaho

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Testing recommended

tested well samples in Idaho exceeded the EPA limit for arsenic (10 ug/L), based on public data from USGS Water Quality Portal and Idaho statewide ground water quality monitoring (IDWR EDMS).

271,819 test results across 15 contaminants from at least 9,476 wells, 1917 to 2026; nitrate has the most at 51,233. Data refreshed September 15, 2026.

Compiled by Nick at Well Water Nerd from public records. How these pages are built

An estimated 396,215 people in Idaho get their drinking water from a private well, per USGS 2015 county water use.

Separately, the USGS national arsenic model estimates that 12% of the 396,215 people on private wells in Idaho draw water above 10 ug/L (the model's range is 10% to 14%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Idaho. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.

Contaminant	Above limit	Samples	Detected	Median	Highest	Limit
Arsenic 1950 to 2026	17%	27,156	86%	2.6	950	10 ug/L EPA limit
Total coliform 2003 to 2023	16%	2,178	17%	0	2,420	0 MPN/100mL EPA limit
Lead 1962 to 2026	9%	17,452	55%	0.09	54,894	15 ug/L EPA limit
Nitrate 1921 to 2026	8%	51,233	91%	1.62	585	10 mg/L EPA limit
Uranium 1954 to 2026	5%	3,125	77%	2	81,600	30 ug/L EPA limit
Fluoride 1942 to 2026	4%	23,365	92%	0.37	233	4 mg/L EPA limit
Radium (226 + 228) 1962 to 2016	<1%	448	53%	0	28.1	5 pCi/L EPA limit
E. coli 1990 to 2016	<1%	5,473	<1%	0	200	0 MPN/100mL EPA limit
Nitrite 1991 to 2023	<1%	6,980	7%	0	27.5	1 mg/L EPA limit
Copper 1962 to 2026	<1%	17,910	66%	0.001	12.9	1.3 mg/L EPA limit
Chloride 1917 to 2026	no limit	37,847	100%	14.8	266,000	250 mg/L nuisance level
Sodium 1924 to 2026	no limit	32,974	100%	16	4,600	20 mg/L health guideline
Iron 1921 to 2026	no limit	22,507	57%	5	851,000	300 ug/L nuisance level
Manganese 1944 to 2026	no limit	21,554	52%	0	517,000	300 ug/L health guideline
Radon 1989 to 2016	no limit	1,617	100%	470	8,040	2,000 pCi/L health guideline

Over time

Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.

Contaminant	before 2000	2000s	2010s	2020s
Nitrate	9%23,875 samples	8%15,519 samples	8%8,485 samples	7%3,354 samples
Arsenic	19%10,027 samples	17%10,399 samples	15%5,153 samples	17%1,577 samples
Fluoride	5%10,829 samples	5%7,995 samples	1%3,472 samples	1%1,069 samples
Copper	<1%8,070 samples	0%5,302 samples	<1%4,184 samples	0%354 samples
Lead	9%9,941 samples	11%4,842 samples	7%2,360 samples	<1%309 samples
Nitrite	<1%2,376 samples	<1%2,597 samples	<1%1,606 samples	<1%401 samples

Lead above the limit in Idaho fell from 7% of 2360 samples in the 2010s to <1% of 309 in the 2020s.

Nitrate, arsenic, fluoride, copper, nitrite have held within a few points between the two most recent periods with enough samples.

What this means

The contaminants most often above their limit here are arsenic (17% of 27,156 samples), total coliform (16% of 2,178 samples), and lead (9% of 17,452 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.

Chloride, Iron, and Manganese are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.

What to test for in Idaho

1
Arsenic
17% of 27,156 local samples were above the limit.
2
Total coliform
16% of 2,178 local samples were above the limit.
3
Lead
9% of 17,452 local samples were above the limit.
4
Nitrate
8% of 51,233 local samples were above the limit.
5
Uranium
5% of 3,125 local samples were above the limit.
6
Fluoride
4% of 23,365 local samples were above the limit.
7
Radium (226 + 228)
<1% of 448 local samples were above the limit.

Test your Idaho well for arsenic, total coliform and lead

Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.

Order the Tap Score well water test kit, from $209 Already tested? Upload the report

Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.

Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.

Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.

Where to get a well tested in Idaho: certified labs, state programs and prices.

Already have results back? Get your lab report read against the Idaho numbers, $29. Every line explained, ranked by what matters, with the fix for each.

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Send me the Idaho report

The numbers above, which tests to order and where, and the treatment that fits the local profile, in one email.

The rock under Idaho

Not a principal aquifer

The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.

Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the state centroid. A single well can sit in a different unit, especially near a boundary.

Official help in Idaho

Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.

Wells, Idaho DEQ
Drinking Water Testing and Certification, Idaho Department of Health and Welfare

Treatment that fits the local profile

Arsenic

Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange

Total coliform

Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system

Lead

Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching

Nitrate

Point-of-use reverse osmosis; Anion exchange; Distillation

Uranium

Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange

Systems we would look at first

Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.

For arsenic

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For arsenic

Whole-house arsenic and uranium filter

whole-house, at the point of entry, about $2,500

Adsorptive iron-based media; sized to your well yield.

For arsenic

Aquasana SmartFlow reverse osmosis

under-sink or countertop, about $225

Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.

For total coliform

Aquasana Rhino Well Water with UV

whole-house, at the point of entry, about $2,871

Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.

For lead

Aquasana Claryum 3-Stage under-sink filter

under-sink or countertop, about $175

Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.

For lead

Acid neutralizing filter

whole-house, at the point of entry, about $1,200

Raises pH so plumbing stops leaching lead and copper.

Common questions

Is there arsenic in well water in Idaho?

Arsenic was detected in 86% of 27,156 public well samples in Idaho, and 17% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.

How high is radon in well water in Idaho?

The median radon level across 1,617 public samples in Idaho was 470 pCi/L, with a high of 8,040 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Idaho?

Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.

Counties in Idaho

Want the numbers themselves? Download the Idaho dataset as CSV, every county and town, with the sources named.

Sources

USGS Water Quality Portal: 189,674 samples in Idaho. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
Idaho statewide ground water quality monitoring (IDWR EDMS): 82,145 samples in Idaho. Ground water quality results from the Idaho Department of Water Resources statewide monitoring program and partner agencies (ISDA, IDEQ, INL), EDMS bulk download. Retrieved September 9, 2026.
USGS national arsenic model (Ayotte 2017): estimated share of 396,215 people on private wells in Idaho above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.

Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.