How hard is the water in Twin Falls County, ID?
18 grains per gallon
A softener will pay its way here.
The median hardness measured in Twin Falls County, ID is 308 mg/L as calcium carbonate, which is 18 gpg. That is very hard on the USGS scale. It comes from 628 samples at 162 sites between 1990 and 2023, 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 12.4 and 22.8 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 18 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 0.1 to 63.7 gpg
The softest single sample on record in Twin Falls County was 1.2 mg/L and the hardest 1,090 mg/L, a 908-fold gap. The top quarter of sites read above 22.8 gpg and the bottom quarter below 12.4 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 18 gpg, rivers and lakes 11.4 gpg
628 groundwater samples from 162 wells put the median at 308 mg/L. 517 surface samples from 12 sites put it at 195.3 mg/L. In Twin Falls County the wells come out 6.6 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 393 lb of salt a year (10 bags of 40 lb, about $71), 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 $171 a year.
Sizing at 18 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,080 | 24,000 | 131 lb |
| 2 | 2,160 | 24,000 | 263 lb |
| 4 | 4,320 | 32,000 | 526 lb |
| 6 | 6,480 | 48,000 | 788 lb |
Twin Falls County against the rest of Idaho
Among the 44 Idaho counties with data, Twin Falls County is number 3 of 44 counting from the hardest. Across the whole country it is harder than 79% of counties.
Softest in Idaho: Valley County at 1.3 gpg. Hardest: Caribou County at 23 gpg. Closest to Twin Falls County: Oneida County (18.6), Bear Lake County (17.3), Franklin County (16.3).