How hard is the water in Lewis and Clark County, MT?
9.8 grains per gallon
A softener is worth it here.
The median hardness measured in Lewis and Clark County, MT is 167 mg/L as calcium carbonate, which is 9.8 gpg. That is hard on the USGS scale. It comes from 1,229 samples at 250 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 7.3 and 14.2 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 9.8 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 Lewis and Clark 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 0.0 to 86.7 gpg
The softest single sample on record in Lewis and Clark County was 0.2 mg/L and the hardest 1,485 mg/L, a 7,425-fold gap. The top quarter of sites read above 14.2 gpg and the bottom quarter below 7.3 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 9.8 gpg, rivers and lakes 6.9 gpg
1,229 groundwater samples from 250 wells put the median at 167 mg/L. 2,288 surface samples from 267 sites put it at 117.5 mg/L. In Lewis and Clark County the wells come out 2.9 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. 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 213 lb of salt a year (6 bags of 40 lb, about $38), 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 $138 a year.
Sizing at 9.8 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 588 | 24,000 | 72 lb |
| 2 | 1,176 | 24,000 | 143 lb |
| 4 | 2,352 | 24,000 | 286 lb |
| 6 | 3,528 | 32,000 | 429 lb |
Lewis and Clark County against the rest of Montana
Among the 56 Montana counties with data, Lewis and Clark County is number 42 of 56 counting from the hardest. Across the whole country it is harder than 50% of counties.
Softest in Montana: Lincoln County at 3.4 gpg. Hardest: Rosebud County at 138.9 gpg. Closest to Lewis and Clark County: Granite County (9.2), Deer Lodge County (8.9), Madison County (10.7).