How hard is the water in Washington County, OR?
8.3 grains per gallon
A softener is worth it here.
The median hardness measured in Washington County, OR is 143 mg/L as calcium carbonate, which is 8.3 gpg. That is hard on the USGS scale. It comes from 318 samples at 110 sites between 1990 and 2025, 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 6.7 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 8.3 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 Washington 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 1.5 to 115.7 gpg
The softest single sample on record in Washington County was 24.9 mg/L and the hardest 1,980 mg/L, an 80-fold gap. The top quarter of sites read above 11.7 gpg and the bottom quarter below 6.7 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 8.3 gpg, rivers and lakes 5.1 gpg
318 groundwater samples from 110 wells put the median at 142.5 mg/L. 1,449 surface samples from 96 sites put it at 88 mg/L. In Washington County the wells come out 3.2 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. 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 24,000-grain unit covers a week between regenerations. Expect about 182 lb of salt a year (5 bags of 40 lb, about $33), 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 $133 a year.
Sizing at 8.3 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 498 | 24,000 | 61 lb |
| 2 | 996 | 24,000 | 121 lb |
| 4 | 1,992 | 24,000 | 242 lb |
| 6 | 2,988 | 24,000 | 364 lb |
Washington County against the rest of Oregon
Among the 36 Oregon counties with data, Washington County is number 9 of 36 counting from the hardest. Across the whole country it is harder than 44% of counties.
Softest in Oregon: Columbia County at 1.4 gpg. Hardest: Malheur County at 17.8 gpg. Closest to Washington County: Multnomah County (8.7), Umatilla County (7.9), Yamhill County (9).