How hard is the water in Rosebud County, MT?
138.9 grains per gallon
A softener will pay its way here.
The median hardness measured in Rosebud County, MT is 2378 mg/L as calcium carbonate, which is 138.9 gpg. That is very hard on the USGS scale. It comes from 9,760 samples at 866 sites between 1990 and 2025, 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 71.9 and 186.3 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 138.9 gpg a softener pays its way here. Before you buy, check the quoted unit's grain capacity against the sizing table below, and ask whether it regenerates on demand, which uses less salt than a timer. Call your utility for its own report if you are on city water.
More on sizing a softener for your household.
From 0.3 to 291.5 gpg
The softest single sample on record in Rosebud County was 5.9 mg/L and the hardest 4,990 mg/L, an 846-fold gap. The top quarter of sites read above 186.3 gpg and the bottom quarter below 71.9 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 138.9 gpg, rivers and lakes 56.8 gpg
9,760 groundwater samples from 866 wells put the median at 2377.5 mg/L. 1,431 surface samples from 112 sites put it at 971.5 mg/L. In Rosebud County the wells come out 82.1 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. A utility here that draws from the river can deliver noticeably different water from a private well next door.
What a softener would cost to run
For a household of 3, the water is harder than a standard single tank handles in a week, so plan on a larger or twin-tank unit. Expect about 3,033 lb of salt a year (76 bags of 40 lb, about $546), 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 $646 a year.
Sizing at 138.9 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 8,334 | 64,000 | 1,014 lb |
| 2 | 16,668 | twin tank | 2,028 lb |
| 4 | 33,336 | twin tank | 4,056 lb |
| 6 | 50,004 | twin tank | 6,084 lb |
Rosebud County against the rest of Montana
Among the 56 Montana counties with data, Rosebud County is the hardest. Across the whole country it is harder than 100% of counties.
Softest in Montana: Lincoln County at 3.4 gpg. Closest to Rosebud County: Sheridan County (98.1), Liberty County (67.8), Powder River County (60.8).