About 36% of the county's 7,915 residents. Rank 21 of 56 in Montana.
95% range 130 to 220 private-well users (2010 base year). Rank 20 of 56 in Montana.
Highest potential (average indoor radon may be greater than 4 pCi/L). EPA says the map should not be used to decide whether an individual home needs testing.
Labs with an address in this county, from the official state lists on this site, matched by ZIP code.
What to test for in Madison County
Private wells are not regulated like public water: EPA advises owners to test their well every year for total coliform bacteria, nitrates, total dissolved solids and pH. Your state's own schedule:
- MSU Extension's Well Educated program calls a bacteria (coliform and E. coli) and nitrate test the minimum test recommended for all private well owners every year. For people who have not tested in recent years, or ever, it suggests a basic domestic analysis (alkalinity, bacteria, conductivity, nitrate and pH). source
Arsenic. USGS estimates that about 170 people using private wells in Madison County had arsenic above 10 µg/L, EPA's limit for public water (2010 base year; 95% range 130 to 220). USGS describes this kind of estimate as useful "for broad screening of the population at risk", so it says nothing certain about any one well. Arsenic has no taste or smell: test for it by name.
Radon. EPA puts Madison County in Zone 1: highest potential (average indoor radon may be greater than 4 pCi/L). That map is about radon in indoor air, and EPA says it should not be used to decide whether an individual home needs testing. If radon is found in your air and you have a well, EPA suggests testing the water too: see radon in well water.
For anything specific to your home (farms nearby, old plumbing, a new baby, a smell or stain), use the which-tests checklist. When the results arrive, check your numbers against EPA's limits.
Show the numbers
| Item | Value | Note |
|---|---|---|
| Missoula County | 4,888 people (2010 base year) | |
| Ravalli County | 3,257 people (2010 base year) | |
| Lewis and Clark County | 2,763 people (2010 base year) | |
| Flathead County | 2,633 people (2010 base year) | |
| Gallatin County | 1,472 people (2010 base year) | |
| Madison County (this county) | 170 people (2010 base year) |
USGS model estimate for broad screening, not a measurement of any well. Only a test tells you about your own well. Source: USGS, Estimated county level domestic well population with arsenic greater than 10 micrograms per liter (Ayotte, Medalie and Qi, 2017), accessed 2026-11-01.
PFAS in public water near Madison County (public supply, not your well)
This is public water data, not your well. A private well draws its own groundwater, which can have more or less PFAS than the public supply nearby. Only a test of your well tells you.
Under EPA’s fifth Unregulated Contaminant Monitoring Rule (UCMR 5), public water systems sampled their water for 29 PFAS between Jan 3, 2023 and Jun 17, 2026. 2 public systems that serve ZIP codes mainly in Madison County reported results. 0 of them had at least one sample with PFOA or PFOS at or above 4.0 ng/L, and 1 had at least one of the 29 PFAS measured at or above its reporting level.
4.0 ng/L (parts per trillion) is both EPA’s UCMR 5 reporting level for PFOA and PFOS and the number in EPA’s 2024 limit for public water. That limit is judged on a running annual average, so one sample at that level is not a violation. EPA proposed changes to its PFAS rules in May 2026: see PFAS in well water for the current status and who should test a well. To test your own well, find a lab certified for PFAS.
Method: a system counts for this county when it reports serving a ZIP code whose largest land part is in this county, so a system serving several counties counts in each. Source: U.S. EPA, UCMR 5 occurrence data (by state), file dated Oct 15, 2026; downloaded Nov 1, 2026.
Testing programs and help in Montana
- MSU Extension's Well Educated program helps well owners test and understand their water. Test kits are available at participating county offices, and guidance on what to test for comes with the kits. source
- MSU's 2026 Well Educated list shows where to pick up a kit. Most pickup points are county Extension offices; others include water quality districts, conservation districts and county environmental health departments. source
- MSU's Statewide Guidance by County map gives testing guidance based on location. Its statewide parameters of concern with exceedances are arsenic, fluoride, nitrate, selenium, uranium, lead and copper. MSU notes that lead and copper typically come from plumbing rather than groundwater. source
Buying a home with a well in Madison County
Loan test (FHA, VA, USDA) in Madison County, MT
- VA. Test results are valid for 90 days from the date the local health authority certifies them, unless the local authority says otherwise. VA’s chapter names no list of contaminants: the water must meet the local health authority’s requirements, or EPA guidelines where it has none. Your lender may ask for specific tests.
- FHA. A well test is required in the situations FHA’s handbook lists, among others, and the report may not be more than 180 days old at disbursement.
- USDA. Guaranteed loans need a water quality test for a private well, done by the local health authority or a state-certified lab, and no more than 180 days old at closing.
Lenders can ask for more (extra tests, a particular lab, who takes the sample): ask your lender before you book. Federal rules as read on Nov 3, 2026 source 1 source 2 source 3. Full comparison: VA, FHA and USDA well water test requirements. Loan test kits sold by mail, with price and days to results: kits compared.
State-certified labs in Madison County
None of the labs on our Montana list has an address in Madison County. Labs elsewhere in the state may take samples by mail or courier: ask the lab, and check the hold time for bacteria before you send one.
Testing by mail from Madison County. Montana State Environmental Laboratory, Chemistry Testing for Private Well sample submission form, July 2025 publishes these prices: Basic Screen (coliform and E. coli presence/absence, nitrate + nitrite, specific conductivity) $55; Metals Screen, WellScan (calcium, magnesium, hardness, sodium, lead, arsenic, copper, uranium) $135; Anion Screen (alkalinity, pH, fluoride, chloride, sulfate) $75 (checked 3 Nov 2026) source. All Montana state-lab prices and how to get a kit.
Labs on the Montana list whose own websites say they take homeowner samples: Alpine Analytical (Helena), Bridger Analytical Laboratory (Bozeman), DPHHS State of Montana Environmental Laboratory (Helena), Montana Environmental Laboratory (Kalispell). Use Check my ZIP to sort labs by distance.
See all Montana labs in the finder and filter by the test you need and by labs that take homeowner samples.
- USGS, Estimated use of water in the United States, county-level data for 2015 (Dieter et al., ver. 2.0, 2018)
- USGS, Estimated county level domestic well population with arsenic greater than 10 micrograms per liter (Ayotte, Medalie and Qi, 2017)
- U.S. EPA, Map of Radon Zones, county list (EPA 402/A-16/001)
- U.S. Census Bureau, 2020 ZCTA to county relationship file (lab ZIP codes to counties)
- Montana DPHHS Water Laboratory Certification Program - Certified Laboratories (page as fetched 2026-11-15 (no date printed))
Filter by the test you need and by labs that take homeowner samples.
Open the finder →