How hard is the water in Jefferson County, CO?
7.6 grains per gallon
A softener is worth it here.
The median hardness measured in Jefferson County, CO is 130 mg/L as calcium carbonate, which is 7.6 gpg. That is hard on the USGS scale. It comes from 293 samples at 133 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 5 and 11.7 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 7.6 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 Jefferson County 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 0.0 to 32.0 gpg
The softest single sample on record in Jefferson County was 0.5 mg/L and the hardest 547 mg/L, a 1,094-fold gap. The top quarter of sites read above 11.7 gpg and the bottom quarter below 5 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 7.6 gpg, rivers and lakes 7.2 gpg
293 groundwater samples from 133 wells put the median at 130 mg/L. 2,918 surface samples from 200 sites put it at 123.5 mg/L. In Jefferson County the wells come out 0.4 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 166 lb of salt a year (5 bags of 40 lb, about $30), 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 $130 a year.
Sizing at 7.6 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 456 | 24,000 | 55 lb |
| 2 | 912 | 24,000 | 111 lb |
| 4 | 1,824 | 24,000 | 222 lb |
| 6 | 2,736 | 24,000 | 333 lb |
Jefferson County against the rest of Colorado
Among the 63 Colorado counties with data, Jefferson County is number 45 of 63 counting from the hardest. Across the whole country it is harder than 41% of counties.
Softest in Colorado: Larimer County at 0.4 gpg. Hardest: Mesa County at 143.7 gpg. Closest to Jefferson County: Lake County (7.7), Rio Grande County (7.7), Elbert County (7).