Quick answer
About 282,000 people in Montana (28.5% of residents) got their water from private wells in 2010, according to USGS estimates. Montana Department of Public Health and Human Services runs the state’s private well guidance. DPHHS's Choose Safe Places program offers free private well water testing to prospective or licensed childcare facilities: one full-panel test per center, plus bacteria and nitrite tests as often as needed. No free program for households is listed.
- People on private wells
- 282,310
- Share of residents
- 28.5%
- Rank among states
- 36th
- Well users modeled above 10 µg/L arsenic
- 8.6%
Where to get your well tested in Montana
- Montana Department of Public Health and Human Services: Montana State Environmental Laboratory, the state’s guidance for private well owners.
- Certified laboratories in Montana. Use a lab certified for drinking water, so results are reliable.
Free or low-cost testing
DPHHS's Choose Safe Places program offers free private well water testing to prospective or licensed childcare facilities: one full-panel test per center, plus bacteria and nitrite tests as often as needed. No free program for households is listed. (source)
Mail-in lab kits are another option when no local lab is convenient. See well water test kits for what home kits can and can’t tell you.
What to test for
- Every year: total coliform bacteria and nitrate.
- Before buying equipment: pH, hardness, iron, manganese and, if there’s a smell, hydrogen sulfide.
- Based on location: arsenic, uranium and radon, PFAS, and lead in older plumbing.
USGS modeling estimates that about 8.6% of Montana’s private well users have water above the 10 µg/L arsenic limit. Arsenic has no taste or smell, so include it in your first test.
Private wells by county
Estimated people relying on private wells in each Montana county in 2010, the share of residents that represents, and the modeled share of well users with arsenic above 10 µg/L. These are USGS model estimates (2010 population), not measurements of any well. Arsenic is hidden for counties with fewer than 500 well users.
| County | People on wells | Share | Arsenic >10 µg/L |
|---|---|---|---|
| Flathead County | 32,689 | 36.0% | 12.4% |
| Missoula County | 26,884 | 24.6% | 8.4% |
| Ravalli County | 25,648 | 63.8% | 6.5% |
| Lewis and Clark County | 20,167 | 31.8% | 11.8% |
| Gallatin County | 19,688 | 22.0% | 11.5% |
| Yellowstone County | 16,347 | 11.0% | 8.0% |
| Lake County | 12,954 | 45.1% | 14.7% |
| Lincoln County | 9,455 | 48.0% | 8.1% |
| Cascade County | 8,666 | 10.7% | 5.2% |
| Jefferson County | 5,947 | 52.1% | 7.7% |
| Park County | 5,568 | 35.6% | 7.0% |
| Sanders County | 5,486 | 48.1% | 13.2% |
Show all 56 counties
| Stillwater County | 5,093 | 55.9% | 6.6% |
| Hill County | 4,953 | 30.8% | 6.4% |
| Carbon County | 4,899 | 48.6% | 5.2% |
| Big Horn County | 4,869 | 37.8% | 6.0% |
| Madison County | 4,488 | 58.4% | 6.5% |
| Richland County | 4,447 | 45.6% | 5.3% |
| Beaverhead County | 4,093 | 44.3% | 5.7% |
| Silver Bow County | 4,022 | 11.8% | 5.3% |
| Fergus County | 3,233 | 27.9% | 3.9% |
| Glacier County | 3,184 | 23.8% | 6.5% |
| Broadwater County | 3,148 | 56.1% | 11.0% |
| Teton County | 2,959 | 48.7% | 4.7% |
| Rosebud County | 2,854 | 30.9% | 5.1% |
| Mineral County | 2,767 | 65.5% | 8.6% |
| Deer Lodge County | 2,736 | 29.4% | 7.1% |
| Custer County | 2,517 | 21.5% | 6.0% |
| Dawson County | 2,446 | 27.3% | 5.0% |
| Musselshell County | 2,194 | 48.3% | 5.0% |
| Roosevelt County | 2,174 | 20.9% | 5.3% |
| Powell County | 2,170 | 30.9% | 8.3% |
| Blaine County | 1,938 | 29.9% | 5.2% |
| Valley County | 1,934 | 26.2% | 13.9% |
| Granite County | 1,687 | 54.8% | 9.0% |
| Chouteau County | 1,679 | 28.9% | 5.2% |
| Phillips County | 1,459 | 34.3% | 6.0% |
| Sweet Grass County | 1,417 | 38.8% | 8.0% |
| Pondera County | 1,311 | 21.3% | 5.1% |
| Judith Basin County | 1,304 | 62.9% | 3.0% |
| Powder River County | 1,107 | 63.5% | 5.0% |
| Sheridan County | 1,044 | 30.8% | 4.5% |
| Wheatland County | 1,028 | 47.4% | 3.0% |
| McCone County | 1,011 | 58.3% | 7.0% |
| Prairie County | 898 | 76.1% | 5.0% |
| Garfield County | 772 | 64.0% | 6.0% |
| Fallon County | 718 | 24.9% | 5.0% |
| Meagher County | 701 | 37.0% | 5.0% |
| Carter County | 669 | 57.7% | 5.0% |
| Daniels County | 622 | 35.5% | 5.0% |
| Liberty County | 574 | 24.5% | 8.0% |
| Golden Valley County | 526 | 59.5% | 4.0% |
| Wibaux County | 416 | 40.9% | – |
| Treasure County | 306 | 42.7% | – |
| Petroleum County | 256 | 51.9% | – |
| Toole County | 188 | 3.5% | – |
Counties with the highest modeled arsenic share: Lake County (14.7%), Valley County (13.9%), Sanders County (13.2%), Flathead County (12.4%), Lewis and Clark County (11.8%).
After you get results
Enter your numbers in the test results tool to see what needs treating and in what order. The guide to reading a well water test explains units and limits.
Common questions
Does Montana offer free well water testing?
DPHHS's Choose Safe Places program offers free private well water testing to prospective or licensed childcare facilities: one full-panel test per center, plus bacteria and nitrite tests as often as needed. No free program for households is listed.
Who oversees private wells in Montana?
Montana Department of Public Health and Human Services (Montana State Environmental Laboratory) publishes guidance for private well owners. Private wells aren’t covered by the federal Safe Drinking Water Act, so testing and treatment are up to the owner.
How many people use private wells in Montana?
USGS estimates about 282,000 people, or 28.5% of the population in 2010. That ranks 36th of the states covered by the estimate.
What should I test my well for in Montana?
Test every year for total coliform bacteria and nitrate, plus pH, hardness, iron and manganese before buying equipment. Arsenic is a known concern in parts of Montana, so add it to the first test.
Sources
- Montana Department of Public Health and Human Services: Montana State Environmental Laboratory
- Montana certified laboratories
- Montana free or low-cost testing
- USGS data release: domestic well locations and populations served, 2000 and 2010 (Johnson, Belitz and Lombard, 2019)
- CDC Environmental Public Health Tracking: private well water data (from USGS)