How hard is the water in Stillwater County, MT?
4.1 grains per gallon
Optional: a softener helps, but plenty of homes skip it.
The median hardness measured in Stillwater County, MT is 70 mg/L as calcium carbonate, which is 4.1 gpg. That is moderately hard on the USGS scale. It comes from 205 samples at 17 sites between 1990 and 2026, drawn from groundwater wells, which is what most taps and private wells in the county draw on.
How much it varies here
Half the sites came in between 3.9 and 5.8 gpg. The whole middle of that range gives the same answer, so a test of your own tap is unlikely to change it. Confidence in the county figure: high (how it is measured).
What to do next
At 4.1 gpg this is your call. Look for white film on glasses and crust on the shower head: if you see little of either, you can live without one. If you do want one, a 24,000-grain unit is enough, so ask for that size rather than a bigger one.
More on when a softener is not worth it.
From 1.1 to 12.3 gpg
The softest single sample on record in Stillwater County was 19.5 mg/L and the hardest 210.3 mg/L, an 11-fold gap. The top quarter of sites read above 5.8 gpg and the bottom quarter below 3.9 gpg.
Wells 4.1 gpg, rivers and lakes 4.3 gpg
205 groundwater samples from 17 wells put the median at 70 mg/L. 221 surface samples from 51 sites put it at 74.2 mg/L. In Stillwater County the rivers and lakes come out 0.2 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. The two sources are close, so the county figure should hold whichever one your tap is on.
What a softener would cost to run
For a household of 3, a 24,000-grain unit covers a week between regenerations. Expect about 89 lb of salt a year (3 bags of 40 lb, about $16), and roughly 2,346 gallons of regeneration water. Installed, most units run $1,000 to $4,500; spread over 15 years with salt, that is about $116 a year.
Sizing at 4.1 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 246 | 24,000 | 30 lb |
| 2 | 492 | 24,000 | 60 lb |
| 4 | 984 | 24,000 | 120 lb |
| 6 | 1,476 | 24,000 | 180 lb |
Stillwater County against the rest of Montana
Among the 56 Montana counties with data, Stillwater County is number 55 of 56 counting from the hardest. Across the whole country it is harder than 26% of counties.
Softest in Montana: Lincoln County at 3.4 gpg. Hardest: Rosebud County at 138.9 gpg. Closest to Stillwater County: Mineral County (4.5), Ravalli County (4.6), Lincoln County (3.4).