Well water in Daniels County, Montana
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Testing strongly recommended
tested well samples in Daniels County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
402 test results across 11 contaminants from at least 45 wells, 1956 to 2021; nitrate has the most at 117. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 652 people in Daniels County get their drinking water from a private well, per USGS 2015 county water use. That is about 37% of residents.
Separately, the USGS national arsenic model estimates that 18% of the 652 people on private wells in Daniels County draw water above 10 ug/L (the model's range is 14% to 22%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Daniels 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 1975 to 2021 | 117 | 94% | 5.1 | 138 | 10 mg/L EPA limit | |
| Fluoride 1975 to 2021 | 51 | 98% | 0.4 | 3.3 | 4 mg/L EPA limit | |
| Arsenic 1976 to 1998 | 12 | 67% | 1 | 3 | 10 ug/L EPA limit | |
| Lead 1976 to 1998 | 10 | 70% | 0 | 0 | 15 ug/L EPA limit | |
| Chloride 1956 to 2021 | no limit | 52 | 100% | 7.1 | 45,100 | 250 mg/L nuisance level |
| Sodium 1975 to 2021 | no limit | 51 | 100% | 52 | 520 | 20 mg/L health guideline |
| Iron 1975 to 2021 | no limit | 49 | 80% | 250 | 31,000 | 300 ug/L nuisance level |
| Manganese 1975 to 2021 | no limit | 47 | 77% | 32 | 750 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Copper (7), Radium (226 + 228) (3), Uranium (3).
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 | 19%74 samples | n/a | n/a | 88%34 samples |
Nitrate above the limit in Daniels County rose from 19% of 74 samples before 2000 to 88% of 34 in the 2020s.
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 addressWhat this means
The contaminants most often above their limit here are nitrate (42% of 117 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 Daniels County
- 1Nitrate42% of 117 local samples were above the limit.
- 2Coliform bacteriaRecommended for every private well, every year.
- 3ChlorideDetected in 100% of local samples.
- 4FluorideDetected in 98% of local samples.
- 5IronDetected in 80% of local samples.
- 6ManganeseDetected in 77% of local samples.
- 7CopperDetected in 57% of local samples.
- 8Volatile organic compounds (VOCs)38 leaking underground storage tank sites on record locally.
Test your Daniels County well for nitrate, coliform bacteria and chloride
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 $209Already 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 Montana: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Daniels County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Daniels County
Lower Tertiary aquifers
Sandstone. Sandstone wells draw from pore space in the rock and tend to be dependable. Iron, manganese and hardness are common, and some sandstones carry arsenic or radium, so a first test should include both.
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 Montana
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.
- Water Resources, Montana DEQ
- Water Laboratory Certification Program, Montana DPHHS
Contamination sources on record in Daniels County
Montana DEQ records 38 leaking underground storage tank sites in Daniels County, among 45 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 38
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 6
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 1
- lined landfill or transfer facility
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Fluoride
Point-of-use reverse osmosis; Activated alumina; Distillation
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 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
Get on the list for a free in-home water test in Daniels County
No water treatment company serves Daniels 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 Daniels County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Daniels County?
Arsenic was detected in 67% of 12 public well samples in Daniels County, and 0% 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 often should I test a private well in Daniels 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 Daniels 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 Montana dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 402 samples in Daniels 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 652 people on private wells in Daniels 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.
- Montana DEQ regulated sites: 45 regulated sites located in Daniels County. Petroleum tank releases, underground storage tank facilities and licensed solid waste facilities from the Montana Department of Environmental Quality. Retrieved September 18, 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.