How hard is the water in Jefferson County, MT?
8.1 grains per gallon
A softener is worth it here.
The median hardness measured in Jefferson County, MT is 138 mg/L as calcium carbonate, which is 8.1 gpg. That is hard on the USGS scale. It comes from 488 samples at 132 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 3.4 and 12.1 gpg. That spread crosses a decision line, so some homes here land on a different answer. A $10 test strip on your own tap settles it. Confidence in the county figure: high (how it is measured).
What to do next
At 8.1 gpg a softener is worth getting, mainly to protect the water heater and cut soap use. Get at least two quotes, ask each installer what grain capacity they are fitting, and check it against the sizing table below. Because Jefferson County straddles a decision line, check your own tap with a $10 test strip before you spend anything.
More on sizing a softener for your household.
From 0.1 to 43.6 gpg
The softest single sample on record in Jefferson County was 1.7 mg/L and the hardest 746 mg/L, a 439-fold gap. The top quarter of sites read above 12.1 gpg and the bottom quarter below 3.4 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 8.1 gpg, rivers and lakes 2.9 gpg
488 groundwater samples from 132 wells put the median at 138 mg/L. 1,604 surface samples from 388 sites put it at 49.3 mg/L. In Jefferson County the wells come out 5.2 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, a 24,000-grain unit covers a week between regenerations. Expect about 176 lb of salt a year (5 bags of 40 lb, about $32), 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 $132 a year.
Sizing at 8.1 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 486 | 24,000 | 59 lb |
| 2 | 972 | 24,000 | 118 lb |
| 4 | 1,944 | 24,000 | 237 lb |
| 6 | 2,916 | 24,000 | 355 lb |
Jefferson County against the rest of Montana
Among the 56 Montana counties with data, Jefferson County is number 47 of 56 counting from the hardest. Across the whole country it is harder than 43% of counties.
Softest in Montana: Lincoln County at 3.4 gpg. Hardest: Rosebud County at 138.9 gpg. Closest to Jefferson County: Missoula County (8.4), Hill County (8.7), Sanders County (7.2).