Water quality by county
in Montana
EPA sampled public water systems across Montana for PFAS under its UCMR 5 programme. Of the 56 counties, 1 have a reading above a federal limit and 34 have not been sampled at all — which is not a clean result, only an absence of one. Each county below shows what was found, at what concentration, and at which utility.
| county | Population | Worst result | Compound |
|---|---|---|---|
| Flathead County | 114,527 | 1.6× | PFOS · 6.6 ng/L |
| Beaverhead County | 10,006 | under the limit | — |
| Big Horn County | 12,796 | under the limit | — |
| Blaine County | 6,903 | not sampled | — |
| Broadwater County | 8,302 | not sampled | — |
| Carbon County | 11,498 | not sampled | — |
| Carter County | 1,399 | not sampled | — |
| Cascade County | 84,523 | under the limit | — |
| Chouteau County | 5,880 | not sampled | — |
| Custer County | 11,964 | under the limit | — |
| Daniels County | 1,625 | not sampled | — |
| Dawson County | 8,731 | under the limit | — |
| Deer Lodge County | 9,811 | under the limit | — |
| Fallon County | 2,946 | not sampled | — |
| Fergus County | 11,862 | under the limit | — |
| Gallatin County | 126,984 | under the limit | — |
| Garfield County | 1,181 | not sampled | — |
| Glacier County | 13,503 | not sampled | — |
| Golden Valley County | 863 | not sampled | — |
| Granite County | 3,602 | not sampled | — |
| Hill County | 16,065 | under the limit | — |
| Jefferson County | 13,304 | not sampled | — |
| Judith Basin County | 2,111 | not sampled | — |
| Lake County | 33,403 | under the limit | — |
| Lewis and Clark County | 75,129 | under the limit | — |
| Liberty County | 1,934 | not sampled | — |
| Lincoln County | 22,184 | under the limit | — |
| Madison County | 9,753 | under the limit | — |
| McCone County | 1,717 | not sampled | — |
| Meagher County | 2,065 | not sampled | — |
| Mineral County | 5,195 | not sampled | — |
| Missoula County | 122,546 | under the limit | — |
| Musselshell County | 5,452 | not sampled | — |
| Park County | 18,074 | under the limit | — |
| Petroleum County | 525 | not sampled | — |
| Phillips County | 4,214 | not sampled | — |
| Pondera County | 6,078 | not sampled | — |
| Powder River County | 1,734 | not sampled | — |
| Powell County | 7,120 | not sampled | — |
| Prairie County | 1,112 | not sampled | — |
| Ravalli County | 48,187 | under the limit | — |
| Richland County | 11,028 | under the limit | — |
| Roosevelt County | 10,197 | not sampled | — |
| Rosebud County | 8,194 | not sampled | — |
| Sanders County | 13,895 | not sampled | — |
| Sheridan County | 3,448 | not sampled | — |
| Silver Bow County | 36,134 | under the limit | — |
| Stillwater County | 9,450 | not sampled | — |
| Sweet Grass County | 3,757 | not sampled | — |
| Teton County | 6,444 | under the limit | — |
| Toole County | 5,153 | under the limit | — |
| Treasure County | 739 | not sampled | — |
| Valley County | 7,434 | not sampled | — |
| Wheatland County | 2,058 | not sampled | — |
| Wibaux County | 911 | not sampled | — |
| Yellowstone County | 171,583 | under the limit | — |