How hard is the water in Contra Costa County, CA?
21.7 grains per gallon
A softener will pay its way here.
The median hardness measured in Contra Costa County, CA is 371 mg/L as calcium carbonate, which is 21.7 gpg. That is very hard on the USGS scale. It comes from 98 samples at 21 sites between 1990 and 2022, drawn from every sampling site in the county, wells and surface water together.
How much it varies here
Half the sites came in between 14.5 and 28.8 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 21.7 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 4.3 to 167.1 gpg
The softest single sample on record in Contra Costa County was 74 mg/L and the hardest 2,860 mg/L, a 39-fold gap. The top quarter of sites read above 28.8 gpg and the bottom quarter below 14.5 gpg.
What a softener would cost to run
For a household of 3, a 32,000-grain unit covers a week between regenerations. Expect about 473 lb of salt a year (12 bags of 40 lb, about $85), 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 $185 a year.
Sizing at 21.7 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,302 | 24,000 | 158 lb |
| 2 | 2,604 | 24,000 | 317 lb |
| 4 | 5,208 | 40,000 | 634 lb |
| 6 | 7,812 | 64,000 | 950 lb |
Contra Costa County against the rest of California
Among the 58 California counties with data, Contra Costa County is number 5 of 58 counting from the hardest. Across the whole country it is harder than 88% of counties.
Softest in California: Sierra County at 1.7 gpg. Hardest: Calaveras County at 98.3 gpg. Closest to Contra Costa County: San Mateo County (20.2), Orange County (18.4), Stanislaus County (16.5).