How hard is the water in Knox County, TN?
12 grains per gallon
A softener will pay its way here.
The median hardness measured in Knox County, TN is 205 mg/L as calcium carbonate, which is 12 gpg. That is very hard on the USGS scale. It comes from 5 samples at 5 sites between 1990 and 2019, 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 11.8 and 13.7 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: medium (how it is measured).
What to do next
At 12 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 8.4 to 15.1 gpg
The softest single sample on record in Knox County was 143 mg/L and the hardest 259 mg/L, a 2-fold gap. The top quarter of sites read above 13.7 gpg and the bottom quarter below 11.8 gpg.
Wells 12 gpg, rivers and lakes 9.5 gpg
5 groundwater samples from 5 wells put the median at 205 mg/L. 471 surface samples from 47 sites put it at 162 mg/L. In Knox County the wells come out 2.5 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 262 lb of salt a year (7 bags of 40 lb, about $47), 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 $147 a year.
Sizing at 12 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 720 | 24,000 | 88 lb |
| 2 | 1,440 | 24,000 | 175 lb |
| 4 | 2,880 | 24,000 | 350 lb |
| 6 | 4,320 | 32,000 | 526 lb |
Knox County against the rest of Tennessee
Among the 95 Tennessee counties with data, Knox County is number 15 of 95 counting from the hardest. Across the whole country it is harder than 58% of counties.
Softest in Tennessee: Fayette County at 0.5 gpg. Hardest: Fentress County at 42.9 gpg. Closest to Knox County: Wilson County (11.9), Rutherford County (11.8), Davidson County (12.2).