How hard is the water in St. Johns County, FL?
18.6 grains per gallon
A softener will pay its way here.
The median hardness measured in St. Johns County, FL is 319 mg/L as calcium carbonate, which is 18.6 gpg. That is very hard on the USGS scale. It comes from 26 samples at 7 sites between 1997 and 2019, 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 12.5 and 23.8 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: medium (how it is measured).
What to do next
At 18.6 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 10.2 to 58.1 gpg
The softest single sample on record in St. Johns County was 173.9 mg/L and the hardest 994 mg/L, a 6-fold gap. The top quarter of sites read above 23.8 gpg and the bottom quarter below 12.5 gpg.
Wells 18.6 gpg, rivers and lakes 11.8 gpg
26 groundwater samples from 7 wells put the median at 318.7 mg/L. 3,570 surface samples from 86 sites put it at 202.3 mg/L. In St. Johns County the wells come out 6.8 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 407 lb of salt a year (11 bags of 40 lb, about $73), 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 $173 a year.
Sizing at 18.6 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,116 | 24,000 | 136 lb |
| 2 | 2,232 | 24,000 | 272 lb |
| 4 | 4,464 | 32,000 | 543 lb |
| 6 | 6,696 | 48,000 | 815 lb |
St. Johns County against the rest of Florida
Among the 67 Florida counties with data, St. Johns County is number 9 of 67 counting from the hardest. Across the whole country it is harder than 81% of counties.
Softest in Florida: Washington County at 0.3 gpg. Hardest: Sarasota County at 32.2 gpg. Closest to St. Johns County: Martin County (18.3), Indian River County (18.9), Collier County (18.1).