How hard is the water in Arlington County, VA?

5.1 grains per gallon

Optional: a softener helps, but plenty of homes skip it.

The median hardness measured in Arlington County, VA is 87 mg/L as calcium carbonate, which is 5.1 gpg. That is moderately hard on the USGS scale. It comes from 413 samples at 4 sites between 1990 and 2026, drawn from every sampling site in the county, wells and surface water together.

How much it varies here

Half the sites came in between 4.7 and 5.6 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: medium (how it is measured).

What to do next

At 5.1 gpg this is your call. Look for white film on glasses and crust on the shower head: if you see little of either, you can live without one. If you do want one, a 24,000-grain unit is enough, so ask for that size rather than a bigger one.

More on when a softener is not worth it.

From 3.9 to 7.0 gpg

The softest single sample on record in Arlington County was 66.1 mg/L and the hardest 120 mg/L, a 2-fold gap. The top quarter of sites read above 5.6 gpg and the bottom quarter below 4.7 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 111 lb of salt a year (3 bags of 40 lb, about $20), 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 $120 a year.

Sizing at 5.1 gpg

Arlington County against the rest of Virginia

Among the 126 Virginia counties with data, Arlington County is number 43 of 126 counting from the hardest. Across the whole country it is harder than 31% of counties.

Softest in Virginia: Isle of Wight County at 0.4 gpg. Hardest: Clarke County at 20.1 gpg. Closest to Arlington County: Botetourt County (5.1), Smyth County (4.9), Hampton city (5.5).