How hard is the water in Pima County, AZ?
9.9 grains per gallon
A softener is worth it here.
The median hardness measured in Pima County, AZ is 170 mg/L as calcium carbonate, which is 9.9 gpg. That is hard on the USGS scale. It comes from 561 samples at 253 sites between 1990 and 2023, 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 6.4 and 15.5 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 9.9 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 Pima 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 0.2 to 150.5 gpg
The softest single sample on record in Pima County was 4 mg/L and the hardest 2,575.5 mg/L, a 644-fold gap. The top quarter of sites read above 15.5 gpg and the bottom quarter below 6.4 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 9.9 gpg, rivers and lakes 8.7 gpg
561 groundwater samples from 253 wells put the median at 170 mg/L. 327 surface samples from 64 sites put it at 149.5 mg/L. In Pima County the wells come out 1.2 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 217 lb of salt a year (6 bags of 40 lb, about $39), 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 $139 a year.
Sizing at 9.9 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 594 | 24,000 | 72 lb |
| 2 | 1,188 | 24,000 | 145 lb |
| 4 | 2,376 | 24,000 | 289 lb |
| 6 | 3,564 | 32,000 | 434 lb |
Pima County against the rest of Arizona
Among the 15 Arizona counties with data, Pima County is number 10 of 15 counting from the hardest. Across the whole country it is harder than 51% of counties.
Softest in Arizona: Navajo County at 9 gpg. Hardest: Yuma County at 28.7 gpg. Closest to Pima County: Cochise County (9.8), Graham County (9.9), La Paz County (9.6).