How hard is the water in Bonneville County, ID?
13.4 grains per gallon
A softener will pay its way here.
The median hardness measured in Bonneville County, ID is 230 mg/L as calcium carbonate, which is 13.4 gpg. That is very hard on the USGS scale. It comes from 178 samples at 40 sites between 1990 and 2018, 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 11.2 and 14.6 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 13.4 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 0.7 to 43.1 gpg
The softest single sample on record in Bonneville County was 12.7 mg/L and the hardest 737 mg/L, a 58-fold gap. The top quarter of sites read above 14.6 gpg and the bottom quarter below 11.2 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 13.4 gpg, rivers and lakes 11.4 gpg
178 groundwater samples from 40 wells put the median at 230 mg/L. 63 surface samples from 3 sites put it at 195.5 mg/L. In Bonneville County the wells come out 2.0 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 293 lb of salt a year (8 bags of 40 lb, about $53), 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 $153 a year.
Sizing at 13.4 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 804 | 24,000 | 98 lb |
| 2 | 1,608 | 24,000 | 196 lb |
| 4 | 3,216 | 24,000 | 391 lb |
| 6 | 4,824 | 40,000 | 587 lb |
Bonneville County against the rest of Idaho
Among the 44 Idaho counties with data, Bonneville County is number 11 of 44 counting from the hardest. Across the whole country it is harder than 64% of counties.
Softest in Idaho: Valley County at 1.3 gpg. Hardest: Caribou County at 23 gpg. Closest to Bonneville County: Jerome County (13.6), Power County (13.8), Owyhee County (12.8).