Well water hardness in Cook County, Minnesota
3.6 gpg moderately hard
Private wells in Cook County typically give moderately hard water: the median well sampled by the U.S. Geological Survey has 3.6 gpg (61 mg/L as CaCO₃).
Wells differ a lot, even next door: one in ten sampled wells had less than 26 mg/L and one in ten more than 116 mg/L. The figure comes from 14 wells and 14 samples taken between 1999 and 2004 (half of them by 2004).
Most samples are older than ten years. Groundwater hardness comes from the rock the well is drilled into and changes slowly, but your own well can be quite different, so treat this as a regional indication and test your water.
What this hardness means for a well household
- Visible kettle scale every few weeks; vinegar or citric acid is enough.
- Water heater and washing machine: some long-term scale; a scale inhibitor slows it.
- Dishwasher: medium salt setting.
- Softener optional; pays off mainly with a gas boiler or tankless heater.
How to test your well in Minnesota
Hardness is only one part of a well test. Federal health agencies advise every private well owner to test regularly:
- Test a private well every year for total coliform bacteria, nitrates, total dissolved solids and pH; test more often if young children, older adults or a pregnant or nursing person live in the home. (US EPA, Protect Your Home's Water)
- Test at least once a year and ask the local health department which other germs or chemicals matter where you live. (CDC, Guidelines for Testing Well Water)
- Test for coliform bacteria and nitrate every year and for arsenic, lead and manganese at least once; test a faucet used for drinking and cooking, and after any treatment. (Minnesota Department of Health, Well water testing (updated 2026-10-19))
Use a certified laboratory: Minnesota Department of Health, accredited laboratory search (private homeowner samples).
Testing is your own responsibility: no state agency samples existing private wells routinely.
What a test costs (Washington County (MN) Public Health, water tests)
| Standard test: coliform bacteria and nitrate | $50 |
| Arsenic | $39 |
| Lead | $39 |
| Hardness | $57 |
| Iron | $39 |
Prices as printed by the lab (2026-10-29); check the current fee before you send a sample. Washington County (MN) Public Health, water tests
If no local lab suits you, mail-in kits from certified labs test a wider panel at home; they cost more than a state or county lab.
Treating hard well water
A softener is optional at this level. Check iron and manganese in your test as well: staining from them is a more common well problem than hardness.
Nearby counties
FAQ
How hard is well water in Cook County, Minnesota?
The median well sampled by the USGS in Cook County has 3.6 gpg (61 mg/L as CaCO₃), which is moderately hard. One in ten wells had less than 26 mg/L and one in ten more than 116 mg/L.
Is my own well the same?
Not necessarily. Hardness depends on the rock layer your well draws from and on its depth, so neighbouring wells can differ by a factor of two or more. Only a test of your own water tells you.
How often should I test my well in Minnesota?
Every year for coliform bacteria, nitrate, total dissolved solids and pH (EPA and CDC advice), and after floods, repairs or a change in taste or smell. Hardness, iron and manganese once, and again before you buy a softener.
Do I need a water softener for my well?
Not essential; a scale inhibitor protects the heater cheaply.
Where does this figure come from?
From 14 samples of 14 wells measured by the U.S. Geological Survey between 1999 and 2004, retrieved from the Water Quality Portal. We publish a county only when at least 10 wells were sampled.
Source and method
Computed by Water Hardness Atlas from USGS National Water Information System samples (characteristic "Hardness, Ca, Mg", sites of type well, samples since 1980), retrieved 2026-10-29 through the Water Quality Portal. For each well we take the median of its samples, then the median of all wells in the county; wells above 1,000 mg/L (oil, gas or mine brines) are left out. USGS data are in the U.S. public domain. Water Quality Portal query
Well water hardness in Minnesota → · Minnesota: tap water by city →