St Johns County, Florida: drinking water report. St. Johns County south of Jacksonville has about 280,000 residents, making it one of the fastest-growing…
St. Johns County south of Jacksonville has about 280,000 residents, making it one of the fastest-growing counties in Florida. The county draws from the Floridan Aquifer, with JEA and St. Johns County Utility Department providing service. The county's rapid conversion from rural to suburban land use is occurring directly over the aquifer recharge zone.
The Floridan Aquifer in St. Johns County naturally contains hydrogen sulfide – the rotten-egg smell familiar to Florida well users – and elevated hardness from the limestone matrix. According to the St. Johns River Water Management District's 2024 assessment, total dissolved solids in the county's production wells average 380 mg/L, with hardness above 200 mg/L. These are not health concerns but affect taste and appliance life.
The former NAS Jacksonville and NAS Cecil Field in neighboring Duval County have PFAS contamination plumes that may extend into northern St. Johns County. Florida DEP's 2024 investigation found PFAS at 6 ppt in one monitoring well in the county's northern border area. Rapid development means more septic systems over the aquifer, contributing nitrate loading.
St. Johns County's rapid growth means the aquifer is serving more people and receiving more potential contamination from development. The natural hydrogen sulfide in the water is unpleasant but not dangerous – a carbon or aeration system eliminates the odor.
Check your water for current data. For hard water, sulfur odor, and emerging PFAS, reverse osmosis addresses all three. Our water filter guide covers systems designed for Florida's aquifer water. Pull your detailed report for local data, and visit our Florida page for statewide context.
Drinking water is one exposure route. These federal datasets also cover St Johns County, FL.
The EPA places St Johns County, FL in Zone 3 - the EPA's lowest-risk category, with a predicted average indoor radon level below 2 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
16% of homes in St Johns County, FL were built before 1980, and 3% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in St Johns County, FL averages 7.8 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide