How hard is the water in San Diego County, CA?
14.3 grains per gallon
A softener will pay its way here.
The median hardness measured in San Diego County, CA is 245 mg/L as calcium carbonate, which is 14.3 gpg. That is very hard on the USGS scale. It comes from 424 samples at 225 sites between 1990 and 2022, 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 7.3 and 29.5 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 14.3 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. Because San Diego 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 280.4 gpg
The softest single sample on record in San Diego County was 3.7 mg/L and the hardest 4,800 mg/L, a 1,297-fold gap. The top quarter of sites read above 29.5 gpg and the bottom quarter below 7.3 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 14.3 gpg, rivers and lakes 27.8 gpg
424 groundwater samples from 225 wells put the median at 244.5 mg/L. 130 surface samples from 32 sites put it at 476.5 mg/L. In San Diego County the rivers and lakes come out 13.5 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. A utility here that draws from the aquifer 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 312 lb of salt a year (8 bags of 40 lb, about $56), 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 $156 a year.
Sizing at 14.3 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 858 | 24,000 | 104 lb |
| 2 | 1,716 | 24,000 | 209 lb |
| 4 | 3,432 | 32,000 | 418 lb |
| 6 | 5,148 | 40,000 | 626 lb |
San Diego County against the rest of California
Among the 58 California counties with data, San Diego County is number 13 of 58 counting from the hardest. Across the whole country it is harder than 67% of counties.
Softest in California: Sierra County at 1.7 gpg. Hardest: Calaveras County at 98.3 gpg. Closest to San Diego County: Sutter County (14.2), Yolo County (14.1), Colusa County (14.5).