How hard is the water in Merrimack County, NH?
3.1 grains per gallon
You do not need a softener here.
The median hardness measured in Merrimack County, NH is 53 mg/L as calcium carbonate, which is 3.1 gpg. That is soft on the USGS scale. It comes from 139 samples at 120 sites between 1990 and 2022, 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 2.2 and 4.6 gpg. That spread crosses a decision line, so some homes here land on a different answer. A $10 test strip on your own tap settles it. Confidence in the county figure: high (how it is measured).
What to do next
You can skip the softener. At 3.1 gpg the most a softener would fix is the odd water spot. If a salesperson in Merrimack County says otherwise, ask to see their reading in grains per gallon and compare it with this one. Because Merrimack County straddles a decision line, check your own tap with a $10 test strip before you spend anything.
More on when a softener is not worth it.
From 0.1 to 10.3 gpg
The softest single sample on record in Merrimack County was 1 mg/L and the hardest 177 mg/L, a 177-fold gap. The top quarter of sites read above 4.6 gpg and the bottom quarter below 2.2 gpg.
Wells 3.1 gpg, rivers and lakes 0.8 gpg
139 groundwater samples from 120 wells put the median at 53 mg/L. 369 surface samples from 66 sites put it at 14.2 mg/L. In Merrimack County the wells come out 2.3 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. The two sources are close, so the county figure should hold whichever one your tap is on.
Merrimack County against the rest of New Hampshire
Among the 10 New Hampshire counties with data, Merrimack County is number 8 of 10 counting from the hardest. Across the whole country it is harder than 22% of counties.
Softest in New Hampshire: Strafford County at 0.8 gpg. Hardest: Rockingham County at 6 gpg. Closest to Merrimack County: Coos County (3.4), Hillsborough County (3.6), Belknap County (3.6).