How hard is the water in District of Columbia, DC?

7.1 grains per gallon

A softener is worth it here.

The median hardness measured in District of Columbia, DC is 121 mg/L as calcium carbonate, which is 7.1 gpg. That is hard on the USGS scale. It comes from 87 samples at 40 sites between 1993 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 3.1 and 9.6 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

At 7.1 gpg a softener is worth getting, mainly to protect the water heater and cut soap use. Get at least two quotes, ask each installer what grain capacity they are fitting, and check it against the sizing table below. Because District of Columbia straddles a decision line, check your own tap with a $10 test strip before you spend anything.

More on sizing a softener for your household.

From 0.6 to 29.0 gpg

The softest single sample on record in District of Columbia was 10.3 mg/L and the hardest 496.5 mg/L, a 48-fold gap. The top quarter of sites read above 9.6 gpg and the bottom quarter below 3.1 gpg. So even here some sites draw water soft enough to need nothing at all.

Wells 7.1 gpg, rivers and lakes 8.4 gpg

87 groundwater samples from 40 wells put the median at 121 mg/L. 33 surface samples from 20 sites put it at 143.8 mg/L. In District of Columbia the rivers and lakes come out 1.3 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. The two sources are close, so the county figure should hold whichever one your tap is on.

What a softener would cost to run

For a household of 3, a 24,000-grain unit covers a week between regenerations. Expect about 154 lb of salt a year (4 bags of 40 lb, about $28), 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 $128 a year.

Sizing at 7.1 gpg

District of Columbia against the rest of the District of Columbia

District of Columbia is the only county in the District of Columbia with enough samples to report. Nationally its water is harder than 39% of the 3,035 counties measured.