How hard is the water in Arapahoe County, CO?
38.6 grains per gallon
A softener will pay its way here.
The median hardness measured in Arapahoe County, CO is 660 mg/L as calcium carbonate, which is 38.6 gpg. That is very hard on the USGS scale. It comes from 658 samples at 117 sites between 1990 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 22.8 and 89.4 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: high (how it is measured).
What to do next
At 38.6 gpg a softener pays its way here. Before you buy, check the quoted unit's grain capacity against the sizing table below, and ask whether it regenerates on demand, which uses less salt than a timer. Call your utility for its own report if you are on city water.
More on sizing a softener for your household.
From 0.2 to 278.1 gpg
The softest single sample on record in Arapahoe County was 2.7 mg/L and the hardest 4,760 mg/L, a 1,763-fold gap. The top quarter of sites read above 89.4 gpg and the bottom quarter below 22.8 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 38.6 gpg, rivers and lakes 27.1 gpg
658 groundwater samples from 117 wells put the median at 660 mg/L. 2,618 surface samples from 140 sites put it at 463.5 mg/L. In Arapahoe County the wells come out 11.5 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. A utility here that draws from the river can deliver noticeably different water from a private well next door.
What a softener would cost to run
For a household of 3, a 64,000-grain unit covers a week between regenerations. Expect about 842 lb of salt a year (22 bags of 40 lb, about $152), 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 $252 a year.
Sizing at 38.6 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 2,316 | 24,000 | 282 lb |
| 2 | 4,632 | 40,000 | 564 lb |
| 4 | 9,264 | 80,000 | 1,127 lb |
| 6 | 13,896 | twin tank | 1,691 lb |
Arapahoe County against the rest of Colorado
Among the 63 Colorado counties with data, Arapahoe County is number 8 of 63 counting from the hardest. Across the whole country it is harder than 97% of counties.
Softest in Colorado: Larimer County at 0.4 gpg. Hardest: Mesa County at 143.7 gpg. Closest to Arapahoe County: Morgan County (38.7), Otero County (39.4), Sedgwick County (42.6).