Well water in Latah County, Idaho

In Latah County, 3% of 638 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from Idaho statewide ground water quality monitoring (IDWR EDMS) and USGS Water Quality Portal.

4,079 test results across 15 contaminants from at least 98 wells, 1955 to 2025; nitrate has the most at 638. Data refreshed September 15, 2026.

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

An estimated 9,118 people in Latah County get their drinking water from a private well, per USGS 2015 county water use. That is about 24% of residents.

Separately, the USGS national arsenic model estimates that 4% of the 9,118 people on private wells in Latah County draw water above 10 ug/L (the model's range is 3% to 5%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Latah County. 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
Nitrate 1955 to 2025	3%	638	66%	0.18	32.4	10 mg/L EPA limit
Arsenic 1990 to 2025	2%	410	35%	0	17	10 ug/L EPA limit
Fluoride 1955 to 2025	0%	446	94%	0.29	2.51	4 mg/L EPA limit
Copper 1990 to 2020	0%	274	51%	0	0.103	1.3 mg/L EPA limit
Lead 1990 to 2016	0%	170	18%	0	4	15 ug/L EPA limit
Nitrite 1991 to 2011	0%	144	4%	0	0.07	1 mg/L EPA limit
E. coli 1990 to 2016	0%	141	0%	0	0	0 MPN/100mL EPA limit
Uranium 1955 to 2025	0%	53	17%	0	3.7	30 ug/L EPA limit
Chloride 1955 to 2025	no limit	453	100%	2.1	100	250 mg/L nuisance level
Sodium 1955 to 2025	no limit	447	100%	12.8	110	20 mg/L health guideline
Iron 1955 to 2025	no limit	440	62%	11.9	8,900	300 ug/L nuisance level
Manganese 1955 to 2025	no limit	429	74%	16.6	1,500	300 ug/L health guideline
Radon 1991 to 2016	no limit	30	100%	465	8,040	2,000 pCi/L health guideline

Sampled fewer than 10 times, too few to summarize: Total coliform (2), Radium (226 + 228) (2).

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	3%231 samples	5%292 samples	0%84 samples	0%31 samples
Fluoride	0%153 samples	0%189 samples	0%73 samples	0%31 samples
Arsenic	3%146 samples	2%163 samples	0%70 samples	3%31 samples
Copper	0%146 samples	0%53 samples	0%71 samples	n/a
Lead	0%146 samples	0%23 samples	n/a	n/a
Nitrite	0%63 samples	0%71 samples	0%10 samples	n/a

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

Closer than the county

See the sampled wells near your address

The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.

Check my address

What this means

The contaminants most often above their limit here are nitrate (3% of 638 samples) and arsenic (2% of 410 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 Latah County

1
Nitrate
3% of 638 local samples were above the limit.
2
Arsenic
2% of 410 local samples were above the limit.
3
Coliform bacteria
Recommended for every private well, every year.
4
Radon
Median local reading is 465 pCi/L.
5
Total coliform
Above the limit in 1 of 2 local samples; too few to quote a rate.
6
Chloride
Detected in 100% of local samples.
7
Fluoride
Detected in 94% of local samples.

Test your Latah County well for nitrate, arsenic and coliform bacteria

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 Latah County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

The rock under Latah County

Columbia Plateau basaltic-rock aquifers

Igneous and metamorphic-rock. Granite and similar crystalline rock hold water only in fractures. Wells are deep and yields modest, and the rock itself is the source of arsenic, radon and uranium, which is why those three head the test list in bedrock country.

Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county 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

Nitrate

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

Arsenic

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

Iron

Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration

Manganese

Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis

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 nitrate

Under-sink reverse osmosis system

under-sink or countertop, about $300

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

For nitrate

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 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 iron

Iron and manganese oxidizing filter

whole-house, at the point of entry, about $1,800

Air-injection or greensand media; fixes staining at the source.

Free, no obligation

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No water treatment company serves Latah County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Latah County, and you get an email naming it first.

Common questions

Is there arsenic in well water in Latah County?

Arsenic was detected in 35% of 410 public well samples in Latah County, and 2% 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 Latah County?

The median radon level across 30 public samples in Latah County was 465 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 Latah County?

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 near Latah County

Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.

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

Sources

Idaho statewide ground water quality monitoring (IDWR EDMS): 2,184 samples in Latah County. 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 Water Quality Portal: 1,895 samples in Latah County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
USGS national arsenic model (Ayotte 2017): estimated share of 9,118 people on private wells in Latah County 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.