How hard is the water in Douglas County, CO?
6.5 grains per gallon
Optional: a softener helps, but plenty of homes skip it.
The median hardness measured in Douglas County, CO is 112 mg/L as calcium carbonate, which is 6.5 gpg. That is moderately hard on the USGS scale. It comes from 50 samples at 36 sites between 1991 and 2026, 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 3.7 and 16.7 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 6.5 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. Because Douglas 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 0.4 to 56.6 gpg
The softest single sample on record in Douglas County was 6.4 mg/L and the hardest 969 mg/L, a 151-fold gap. The top quarter of sites read above 16.7 gpg and the bottom quarter below 3.7 gpg.
Wells 6.5 gpg, rivers and lakes 5.8 gpg
50 groundwater samples from 36 wells put the median at 111.5 mg/L. 1,445 surface samples from 95 sites put it at 98.5 mg/L. In Douglas County the wells come out 0.7 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.
What a softener would cost to run
For a household of 3, a 24,000-grain unit covers a week between regenerations. Expect about 142 lb of salt a year (4 bags of 40 lb, about $26), 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 $126 a year.
Sizing at 6.5 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 390 | 24,000 | 47 lb |
| 2 | 780 | 24,000 | 95 lb |
| 4 | 1,560 | 24,000 | 190 lb |
| 6 | 2,340 | 24,000 | 285 lb |
Douglas County against the rest of Colorado
Among the 63 Colorado counties with data, Douglas County is number 49 of 63 counting from the hardest. Across the whole country it is harder than 37% of counties.
Softest in Colorado: Larimer County at 0.4 gpg. Hardest: Mesa County at 143.7 gpg. Closest to Douglas County: Dolores County (6.7), Custer County (6.3), Gilpin County (6.3).