Well water in St. Johns County, Florida
In St. Johns County, <1% of 242 tested well samples exceeded the EPA limit for arsenic (10 ug/L), based on public data from USGS Water Quality Portal.
2,378 test results across 15 contaminants from at least 62 wells, 1970 to 2025; chloride has the most at 521. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 54,445 people in St. Johns County get their drinking water from a private well, per USGS 2015 county water use. That is about 24% of residents.
Separately, the USGS national arsenic model estimates that 2% of the 54,445 people on private wells in St. Johns County draw water above 10 ug/L (the model's range is 1% to 3%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside St. Johns County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| Arsenic 2009 to 2024 | 242 | 100% | 0.5 | 11.2 | 10 ug/L EPA limit | |
| Copper 2009 to 2024 | 242 | 100% | 0.001 | 0.21 | 1.3 mg/L EPA limit | |
| Lead 2009 to 2024 | 242 | 100% | 0.05 | 3.75 | 15 ug/L EPA limit | |
| Fluoride 1981 to 2025 | 224 | 100% | 0.55 | 1.3 | 4 mg/L EPA limit | |
| Chloride 1970 to 2025 | no limit | 521 | 100% | 24 | 19994 | 250 mg/L nuisance level |
| Sodium 1977 to 2025 | no limit | 412 | 100% | 22.4 | 12019 | 20 mg/L health guideline |
| Manganese 1997 to 2024 | no limit | 243 | 100% | 4.52 | 1134 | 300 ug/L health guideline |
| Iron 1997 to 2024 | no limit | 243 | 100% | 51 | 37523 | 300 ug/L nuisance level |
Sampled fewer than 10 times, too few to summarize: Nitrate (2), Radium (226 + 228) (2), PFOA (1), PFOS (1), E. coli (1), Uranium (1), Radon (1).
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Arsenic | n/a | 0%12 samples | 0%105 samples | <1%125 samples |
| Copper | n/a | 0%12 samples | 0%105 samples | 0%125 samples |
| Lead | n/a | 0%12 samples | 0%105 samples | 0%125 samples |
| Fluoride | 0%57 samples | n/a | 0%93 samples | 0%74 samples |
Arsenic, copper, lead, fluoride have held within a few points between the two most recent periods with enough samples.
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
The contaminants most often above their limit here are arsenic (<1% of 242 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Chloride, Manganese, and Iron are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in St. Johns County
- 1Arsenic<1% of 242 local samples were above the limit.
- 2Coliform bacteriaRecommended for every private well, every year.
- 3RadonMedian local reading is 173 pCi/L.
- 4NitrateRecommended for every private well, especially near farms or septic systems.
- 5FluorideDetected in 100% of local samples.
- 6ManganeseDetected in 100% of local samples.
- 7IronDetected in 100% of local samples.
- 8Volatile organic compounds (VOCs)348 leaking underground storage tank sites on record locally.
Test your St. Johns County well for arsenic, coliform bacteria and radon
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in Florida: certified labs, state programs and prices.
Already have results back? Get your lab report read against the St. Johns County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under St. Johns County
Surficial aquifer system
Unconsolidated sand and gravel. Wells in sand and gravel are usually shallow and productive, and they recharge quickly from the surface. That makes them the most exposed to nitrate, bacteria and anything spilled nearby, and the least likely to carry arsenic or radon from the rock.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Florida
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
- Private Well Water Testing, Florida Department of Health
- NELAP Certified Laboratory Search, Florida DEP
Contamination sources on record in St. Johns County
FDEP records 348 leaking underground storage tank sites in St. Johns County, among 432 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 348
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 84
- other remediation projects
Treatment that fits the local profile
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Manganese
Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Chloride
Point-of-use reverse osmosis; Distillation
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For arsenic
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
For arsenic
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
For manganese
Iron and manganese oxidizing filter
whole-house, at the point of entry, about $1,800
Air-injection or greensand media; fixes staining at the source.
Free, no obligation
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Common questions
Is there arsenic in well water in St. Johns County?
Arsenic was detected in 100% of 242 public well samples in St. Johns County, and <1% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How often should I test a private well in St. Johns County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Counties near St. Johns County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the Florida dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 2,378 samples in St. Johns County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 54,445 people on private wells in St. Johns County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- FDEP regulated sites: 432 regulated sites located in St. Johns County. Petroleum contamination discharges and cleanup sites from the Florida Department of Environmental Protection. Retrieved September 17, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.