How hard is the water in Mercer County, MO?
7.9 grains per gallon
A softener is worth it here.
The median hardness measured in Mercer County, MO is 136 mg/L as calcium carbonate, which is 7.9 gpg. That is hard on the USGS scale. It comes from 156 samples at 5 sites between 1998 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 3.9 and 11.8 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: medium (how it is measured).
What to do next
At 7.9 gpg a softener is worth getting, mainly to protect the water heater and cut soap use. Get at least two quotes, ask each installer what grain capacity they are fitting, and check it against the sizing table below. Because Mercer County straddles a decision line, check your own tap with a $10 test strip before you spend anything.
More on sizing a softener for your household.
From 2.6 to 12.2 gpg
The softest single sample on record in Mercer County was 44.3 mg/L and the hardest 209 mg/L, a 5-fold gap. The top quarter of sites read above 11.8 gpg and the bottom quarter below 3.9 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 7.9 gpg, rivers and lakes 7.8 gpg
1 groundwater samples from 1 wells put the median at 136 mg/L. 155 surface samples from 4 sites put it at 134.1 mg/L. In Mercer County the wells come out 0.1 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 174 lb of salt a year (5 bags of 40 lb, about $31), 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 $131 a year.
Sizing at 7.9 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 474 | 24,000 | 58 lb |
| 2 | 948 | 24,000 | 115 lb |
| 4 | 1,896 | 24,000 | 231 lb |
| 6 | 2,844 | 24,000 | 346 lb |
Mercer County against the rest of Missouri
Among the 110 Missouri counties with data, Mercer County is number 102 of 110 counting from the hardest. Across the whole country it is harder than 42% of counties.
Softest in Missouri: Livingston County at 4.1 gpg. Hardest: Reynolds County at 96.7 gpg. Closest to Mercer County: Audrain County (8.6), Ralls County (8.8), Scott County (7).