How hard is the water in Jerome County, ID?
13.6 grains per gallon
A softener will pay its way here.
The median hardness measured in Jerome County, ID is 233 mg/L as calcium carbonate, which is 13.6 gpg. That is very hard on the USGS scale. It comes from 372 samples at 105 sites between 1990 and 2020, 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 10.4 and 15 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 13.6 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. Because Jerome 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 0.2 to 23.1 gpg
The softest single sample on record in Jerome County was 3.3 mg/L and the hardest 395 mg/L, a 120-fold gap. The top quarter of sites read above 15 gpg and the bottom quarter below 10.4 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 13.6 gpg, rivers and lakes 13.4 gpg
372 groundwater samples from 105 wells put the median at 233 mg/L. 10 surface samples from 2 sites put it at 230 mg/L. In Jerome County the wells come out 0.2 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. 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 297 lb of salt a year (8 bags of 40 lb, about $54), 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 $154 a year.
Sizing at 13.6 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 816 | 24,000 | 99 lb |
| 2 | 1,632 | 24,000 | 199 lb |
| 4 | 3,264 | 24,000 | 397 lb |
| 6 | 4,896 | 40,000 | 596 lb |
Jerome County against the rest of Idaho
Among the 44 Idaho counties with data, Jerome County is number 10 of 44 counting from the hardest. Across the whole country it is harder than 65% of counties.
Softest in Idaho: Valley County at 1.3 gpg. Hardest: Caribou County at 23 gpg. Closest to Jerome County: Bonneville County (13.4), Power County (13.8), Owyhee County (12.8).