How hard is the water in Carter County, OK?
18.7 grains per gallon
A softener will pay its way here.
The median hardness measured in Carter County, OK is 320 mg/L as calcium carbonate, which is 18.7 gpg. That is very hard on the USGS scale. It comes from 340 samples at 9 sites between 1990 and 2025, drawn from every sampling site in the county, wells and surface water together.
How much it varies here
Half the sites came in between 12.5 and 31.2 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 18.7 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 10.8 to 33.5 gpg
The softest single sample on record in Carter County was 185.5 mg/L and the hardest 574 mg/L, a 3-fold gap. The top quarter of sites read above 31.2 gpg and the bottom quarter below 12.5 gpg.
Wells 19.9 gpg, rivers and lakes 13.7 gpg
2 groundwater samples from 2 wells put the median at 340.5 mg/L. 338 surface samples from 7 sites put it at 234 mg/L. In Carter County the wells come out 6.2 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. 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 408 lb of salt a year (11 bags of 40 lb, about $73), 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 $173 a year.
Sizing at 18.7 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,122 | 24,000 | 137 lb |
| 2 | 2,244 | 24,000 | 273 lb |
| 4 | 4,488 | 32,000 | 546 lb |
| 6 | 6,732 | 48,000 | 819 lb |
Carter County against the rest of Oklahoma
Among the 77 Oklahoma counties with data, Carter County is number 28 of 77 counting from the hardest. Across the whole country it is harder than 81% of counties.
Softest in Oklahoma: McCurtain County at 0.8 gpg. Hardest: Greer County at 125 gpg. Closest to Carter County: Marshall County (18.6), Murray County (19.2), Garvin County (17.9).