How hard is the water in St. Charles County, MO?
17.2 grains per gallon
A softener will pay its way here.
The median hardness measured in St. Charles County, MO is 295 mg/L as calcium carbonate, which is 17.2 gpg. That is very hard on the USGS scale. It comes from 151 samples at 77 sites between 1990 and 2026, 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 14.1 and 24 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 17.2 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 0.6 to 84.1 gpg
The softest single sample on record in St. Charles County was 9.5 mg/L and the hardest 1,440 mg/L, a 152-fold gap. The top quarter of sites read above 24 gpg and the bottom quarter below 14.1 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 17.2 gpg, rivers and lakes 11.1 gpg
151 groundwater samples from 77 wells put the median at 295 mg/L. 293 surface samples from 58 sites put it at 190 mg/L. In St. Charles County the wells come out 6.1 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. 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 376 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 17.2 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,032 | 24,000 | 126 lb |
| 2 | 2,064 | 24,000 | 251 lb |
| 4 | 4,128 | 32,000 | 502 lb |
| 6 | 6,192 | 48,000 | 753 lb |
St. Charles County against the rest of Missouri
Among the 110 Missouri counties with data, St. Charles County is number 10 of 110 counting from the hardest. Across the whole country it is harder than 77% of counties.
Softest in Missouri: Livingston County at 4.1 gpg. Hardest: Reynolds County at 96.7 gpg. Closest to St. Charles County: Benton County (16.9), Maries County (16.6), Cape Girardeau County (16.4).