How hard is the water in St. Louis city, MO?

12.1 grains per gallon

A softener will pay its way here.

The median hardness measured in St. Louis city, MO is 208 mg/L as calcium carbonate, which is 12.1 gpg. That is very hard on the USGS scale. It comes from 49 samples at 2 sites between 1993 and 2011, drawn from every sampling site in the county, wells and surface water together.

How much it varies here

Half the sites came in between 11.6 and 12.7 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: low (how it is measured).

What to do next

At 12.1 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 13.2 gpg

The softest single sample on record in St. Louis city was 190 mg/L and the hardest 225.5 mg/L, a 1-fold gap. The top quarter of sites read above 12.7 gpg and the bottom quarter below 11.6 gpg.

What a softener would cost to run

For a household of 3, a 24,000-grain unit covers a week between regenerations. Expect about 265 lb of salt a year (7 bags of 40 lb, about $48), 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 $148 a year.

Sizing at 12.1 gpg

St. Louis city against the rest of Missouri

Among the 110 Missouri counties with data, St. Louis city is number 48 of 110 counting from the hardest. Across the whole country it is harder than 59% of counties.

Softest in Missouri: Livingston County at 4.1 gpg. Hardest: Reynolds County at 96.7 gpg. Closest to St. Louis city: Jasper County (12.1), Clark County (12.1), Polk County (12.2).