Private Well Water Testing in Montana
County-by-county USGS area-risk estimates for private wells across Montana — arsenic exceedance probability and private-well population — plus how to test your own well at a Montana-certified laboratory.
Montana private-well risk summary
Counties covered
56
Montana counties with modeled risk data.
People on private wells
area estimate280,212
estimated across covered Montana counties.
Average arsenic risk
area estimate6%
average modeled chance a well exceeds 10 µg/L arsenic across covered counties.
Montana counties
- Flathead County9% arsenic exceedance (area estimate)32,679 people on private wells
- Missoula County7% arsenic exceedance (area estimate)26,849 people on private wells
- Ravalli County6% arsenic exceedance (area estimate)25,679 people on private wells
- Lewis and Clark County7% arsenic exceedance (area estimate)20,072 people on private wells
- Gallatin County9% arsenic exceedance (area estimate)19,707 people on private wells
- Yellowstone County7% arsenic exceedance (area estimate)16,258 people on private wells
- Lake County13% arsenic exceedance (area estimate)12,921 people on private wells
- Lincoln County8% arsenic exceedance (area estimate)9,440 people on private wells
- Cascade County4% arsenic exceedance (area estimate)8,678 people on private wells
- Jefferson County7% arsenic exceedance (area estimate)5,957 people on private wells
- Park County6% arsenic exceedance (area estimate)5,555 people on private wells
- Sanders County15% arsenic exceedance (area estimate)5,478 people on private wells
- Stillwater County6% arsenic exceedance (area estimate)5,093 people on private wells
- Carbon County5% arsenic exceedance (area estimate)4,833 people on private wells
- Big Horn County6% arsenic exceedance (area estimate)4,780 people on private wells
- Hill County7% arsenic exceedance (area estimate)4,755 people on private wells
- Madison County6% arsenic exceedance (area estimate)4,411 people on private wells
- Richland County5% arsenic exceedance (area estimate)4,362 people on private wells
- Beaverhead County6% arsenic exceedance (area estimate)4,055 people on private wells
- Silver Bow County5% arsenic exceedance (area estimate)4,043 people on private wells
- Fergus County4% arsenic exceedance (area estimate)3,207 people on private wells
- Glacier County6% arsenic exceedance (area estimate)3,161 people on private wells
- Broadwater County11% arsenic exceedance (area estimate)3,109 people on private wells
- Teton County4% arsenic exceedance (area estimate)2,946 people on private wells
- Rosebud County5% arsenic exceedance (area estimate)2,804 people on private wells
- Mineral County8% arsenic exceedance (area estimate)2,792 people on private wells
- Deer Lodge County7% arsenic exceedance (area estimate)2,591 people on private wells
- Custer County6% arsenic exceedance (area estimate)2,502 people on private wells
- Dawson County5% arsenic exceedance (area estimate)2,453 people on private wells
- Musselshell County5% arsenic exceedance (area estimate)2,181 people on private wells
- Powell County9% arsenic exceedance (area estimate)2,146 people on private wells
- Roosevelt County5% arsenic exceedance (area estimate)2,136 people on private wells
- Valley County12% arsenic exceedance (area estimate)1,925 people on private wells
- Blaine County5% arsenic exceedance (area estimate)1,868 people on private wells
- Granite County9% arsenic exceedance (area estimate)1,681 people on private wells
- Phillips County6% arsenic exceedance (area estimate)1,394 people on private wells
- Sweet Grass County8% arsenic exceedance (area estimate)1,392 people on private wells
- Chouteau County6% arsenic exceedance (area estimate)1,358 people on private wells
- Judith Basin County3% arsenic exceedance (area estimate)1,250 people on private wells
- Pondera County5% arsenic exceedance (area estimate)1,202 people on private wells
- Powder River County5% arsenic exceedance (area estimate)1,071 people on private wells
- Sheridan County5% arsenic exceedance (area estimate)1,030 people on private wells
- Wheatland County3% arsenic exceedance (area estimate)1,024 people on private wells
- McCone County7% arsenic exceedance (area estimate)993 people on private wells
- Prairie County5% arsenic exceedance (area estimate)899 people on private wells
- Garfield County6% arsenic exceedance (area estimate)713 people on private wells
- Fallon County5% arsenic exceedance (area estimate)697 people on private wells
- Meagher County5% arsenic exceedance (area estimate)684 people on private wells
- Carter County5% arsenic exceedance (area estimate)633 people on private wells
- Daniels County5% arsenic exceedance (area estimate)611 people on private wells
- Liberty County8% arsenic exceedance (area estimate)560 people on private wells
- Golden Valley County4% arsenic exceedance (area estimate)522 people on private wells
- Wibaux County4% arsenic exceedance (area estimate)361 people on private wells
- Treasure County5% arsenic exceedance (area estimate)298 people on private wells
- Petroleum County4% arsenic exceedance (area estimate)245 people on private wells
- Toole County7% arsenic exceedance (area estimate)168 people on private wells
Find a Montana-certified testing lab
Get your well tested at a Montana-certified laboratory. We list certification programs by state.
These figures are USGS area estimates: statistical groundwater models describing how likely elevated contaminant levels are across a county. They are not designed to predict the concentration in any single well. Only testing your own well reveals its water quality.
By TapWaterData Editorial
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