Well water hardness in Coos County, New Hampshire
4.3 gpg moderately hard
Private wells in Coos County typically give moderately hard water: the median well sampled by the U.S. Geological Survey has 4.3 gpg (74 mg/L as CaCO₃).
Wells differ a lot, even next door: one in ten sampled wells had less than 34 mg/L and one in ten more than 143 mg/L. The figure comes from 158 wells and 171 samples taken between 1984 and 2019 (half of them by 1989).
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 New Hampshire
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)
- Have the water tested by an accredited lab every three to five years, adding radiological tests on the same schedule, and sooner after well construction or repairs or any change in taste, smell or appearance. (University of New Hampshire Extension (2019))
Your county health department can tell you which certified laboratories accept private well samples.
New Hampshire does not require testing of existing private wells at sale; RSA 477:4-a only requires sellers to give buyers a notice that encourages them to consult the NHDES private well testing recommendations.
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 Coos County, New Hampshire?
The median well sampled by the USGS in Coos County has 4.3 gpg (74 mg/L as CaCO₃), which is moderately hard. One in ten wells had less than 34 mg/L and one in ten more than 143 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 New Hampshire?
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 171 samples of 158 wells measured by the U.S. Geological Survey between 1984 and 2019, 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