How hard is the water in Martin County, MN?

12.4 grains per gallon

A softener will pay its way here.

The median hardness measured in Martin County, MN is 213 mg/L as calcium carbonate, which is 12.4 gpg. That is very hard on the USGS scale. It comes from 105 samples at 24 sites between 1991 and 2025, drawn from every sampling site in the county, wells and surface water together.

How much it varies here

Half the sites came in between 11.1 and 19.3 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 12.4 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 8.8 to 26.0 gpg

The softest single sample on record in Martin County was 151 mg/L and the hardest 445 mg/L, a 3-fold gap. The top quarter of sites read above 19.3 gpg and the bottom quarter below 11.1 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 271 lb of salt a year (7 bags of 40 lb, about $49), 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 $149 a year.

Sizing at 12.4 gpg

Martin County against the rest of Minnesota

Among the 87 Minnesota counties with data, Martin County is number 68 of 87 counting from the hardest. Across the whole country it is harder than 60% of counties.

Softest in Minnesota: Lake County at 1.3 gpg. Hardest: Traverse County at 42.6 gpg. Closest to Martin County: Le Sueur County (12.3), Cass County (13), Douglas County (13).