How hard is the water in Mercer County, IL?
17.3 grains per gallon
A softener will pay its way here.
The median hardness measured in Mercer County, IL is 296 mg/L as calcium carbonate, which is 17.3 gpg. That is very hard on the USGS scale. It comes from 113 samples at 10 sites between 1990 and 2014, drawn from every sampling site in the county, wells and surface water together.
How much it varies here
Half the sites came in between 14 and 17.8 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 17.3 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 11.1 to 21.4 gpg
The softest single sample on record in Mercer County was 190 mg/L and the hardest 365.5 mg/L, a 2-fold gap. The top quarter of sites read above 17.8 gpg and the bottom quarter below 14 gpg.
Wells 12.6 gpg, rivers and lakes 17.6 gpg
3 groundwater samples from 3 wells put the median at 216 mg/L. 110 surface samples from 7 sites put it at 302 mg/L. In Mercer County the rivers and lakes come out 5.0 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. A utility here that draws from the aquifer 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 378 lb of salt a year (10 bags of 40 lb, about $68), 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 $168 a year.
Sizing at 17.3 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,038 | 24,000 | 126 lb |
| 2 | 2,076 | 24,000 | 253 lb |
| 4 | 4,152 | 32,000 | 505 lb |
| 6 | 6,228 | 48,000 | 758 lb |
Mercer County against the rest of Illinois
Among the 102 Illinois counties with data, Mercer County is number 52 of 102 counting from the hardest. Across the whole country it is harder than 77% of counties.
Softest in Illinois: Pope County at 4.3 gpg. Hardest: Cook County at 34.8 gpg. Closest to Mercer County: Rock Island County (17.3), Cumberland County (17.2), Mason County (17.5).