How hard is the water in Mercer County, OH?
20.7 grains per gallon
A softener will pay its way here.
The median hardness measured in Mercer County, OH is 354 mg/L as calcium carbonate, which is 20.7 gpg. That is very hard on the USGS scale. It comes from 757 samples at 85 sites between 1993 and 2024, drawn from every sampling site in the county, wells and surface water together.
How much it varies here
Half the sites came in between 16.2 and 27.3 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 20.7 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 8.7 to 56.9 gpg
The softest single sample on record in Mercer County was 148.5 mg/L and the hardest 974 mg/L, a 7-fold gap. The top quarter of sites read above 27.3 gpg and the bottom quarter below 16.2 gpg.
Wells 51 gpg, rivers and lakes 20.1 gpg
5 groundwater samples from 3 wells put the median at 872.5 mg/L. 713 surface samples from 76 sites put it at 344.8 mg/L. In Mercer County the wells come out 30.9 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 32,000-grain unit covers a week between regenerations. Expect about 452 lb of salt a year (12 bags of 40 lb, about $81), 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 $181 a year.
Sizing at 20.7 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,242 | 24,000 | 151 lb |
| 2 | 2,484 | 24,000 | 302 lb |
| 4 | 4,968 | 40,000 | 604 lb |
| 6 | 7,452 | 64,000 | 907 lb |
Mercer County against the rest of Ohio
Among the 88 Ohio counties with data, Mercer County is number 26 of 88 counting from the hardest. Across the whole country it is harder than 85% of counties.
Softest in Ohio: Scioto County at 5.7 gpg. Hardest: Perry County at 113.3 gpg. Closest to Mercer County: Licking County (20.5), Ross County (20.9), Pike County (20.9).