How hard is the water in San Francisco County, CA?
13.1 grains per gallon
A softener will pay its way here.
The median hardness measured in San Francisco County, CA is 224 mg/L as calcium carbonate, which is 13.1 gpg. That is very hard on the USGS scale. It comes from 15 samples at 14 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 10.9 and 14.1 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: medium (how it is measured).
What to do next
At 13.1 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 8.2 to 40.1 gpg
The softest single sample on record in San Francisco County was 141 mg/L and the hardest 686 mg/L, a 5-fold gap. The top quarter of sites read above 14.1 gpg and the bottom quarter below 10.9 gpg.
Wells 13.1 gpg, rivers and lakes 13.5 gpg
15 groundwater samples from 14 wells put the median at 223.5 mg/L. 188 surface samples from 11 sites put it at 231 mg/L. In San Francisco County the rivers and lakes come out 0.4 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. 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 285 lb of salt a year (8 bags of 40 lb, about $51), 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 $151 a year.
Sizing at 13.1 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 786 | 24,000 | 96 lb |
| 2 | 1,572 | 24,000 | 191 lb |
| 4 | 3,144 | 24,000 | 383 lb |
| 6 | 4,716 | 40,000 | 574 lb |
San Francisco County against the rest of California
Among the 58 California counties with data, San Francisco County is number 21 of 58 counting from the hardest. Across the whole country it is harder than 62% of counties.
Softest in California: Sierra County at 1.7 gpg. Hardest: Calaveras County at 98.3 gpg. Closest to San Francisco County: Riverside County (13.1), Glenn County (13.3), Santa Cruz County (12.9).