How hard is the water in Johnson County, TN?
2.3 grains per gallon
You do not need a softener here.
The median hardness measured in Johnson County, TN is 40 mg/L as calcium carbonate, which is 2.3 gpg. That is soft on the USGS scale. It comes from 474 samples at 75 sites between 1990 and 2018, drawn from every sampling site in the county, wells and surface water together.
How much it varies here
Half the sites came in between 0.9 and 4 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
You can skip the softener. At 2.3 gpg the most a softener would fix is the odd water spot. If a salesperson in Johnson County says otherwise, ask to see their reading in grains per gallon and compare it with this one. Because Johnson County straddles a decision line, check your own tap with a $10 test strip before you spend anything.
More on when a softener is not worth it.
From 0.1 to 8.0 gpg
The softest single sample on record in Johnson County was 1.5 mg/L and the hardest 137 mg/L, a 91-fold gap. The top quarter of sites read above 4 gpg and the bottom quarter below 0.9 gpg.
Wells 4 gpg, rivers and lakes 2.3 gpg
3 groundwater samples from 3 wells put the median at 68.8 mg/L. 471 surface samples from 72 sites put it at 39 mg/L. In Johnson County the wells come out 1.7 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.
Johnson County against the rest of Tennessee
Among the 95 Tennessee counties with data, Johnson County is number 77 of 95 counting from the hardest. Across the whole country it is harder than 18% of counties.
Softest in Tennessee: Fayette County at 0.5 gpg. Hardest: Fentress County at 42.9 gpg. Closest to Johnson County: Madison County (2.3), Haywood County (2.3), Franklin County (2.4).