Typical values from 57 sampled wells in St. Johns County · Full groundwater profile
What Are You Noticing in Your Water?
Pre-selected from St. Johns County well data. Untick anything you do not notice in your own water.
Based on the contaminants most commonly reported in this region. Always confirm with a certified lab water test before buying equipment.
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Explore St. Johns County and nearby counties
Most homes in St. Johns County, in Northeast Florida, are on public water, but about one in ten still are not: 9.7% of built parcels, roughly 9,834 properties, draw drinking water from an onsite private well, according to the Florida Department of Health’s 2022 inventory.
St. Johns County, home to St. Augustine, lies between the St. Johns River and the Atlantic coast, and private wells here may tap either the shallow surficial aquifer or the deeper Floridan Aquifer. That geology shapes which well water problems show up most often here.
In this guide
Groundwater Profile: St. Johns County
Most groundwater pumped in St. Johns County comes from the Floridan Aquifer (USGS, 2015 withdrawals). Across 57 sampled wells, the median hardness is 23.2 gpg, which the USGS classes as very hard. It applies to wells across St. Johns County, including around St. Augustine, St. Augustine Beach and Marineland.
What shows up in local well samples:
- HardnessMedian 23.2 gpg; 90% of 57 sampled wells above 7 gpg
Calcium and magnesium dissolved from limestone. Leaves scale on fixtures and water heaters and reduces soap lather. Not a health risk.
Water softener sizing - Chloride (salinity)Median chloride 130 mg/L
A salty taste and faster corrosion, often a sign of saltwater intrusion. The EPA aesthetic guideline is 250 mg/L.
Reverse osmosis guide
Hydrogen sulfide (the rotten-egg smell) was measured in only 0 St. Johns County wells, too few to say how common it is. Limited local data (fewer than 20 samples): individual well testing recommended. If you notice the smell, a sulfide test confirms it.
How St. Johns County Compares to Florida and the U.S.
See How St. Johns County Compares to Florida & the US
| Share of wells with… | St. Johns CountySt. Johns | FloridaFL | United StatesUS |
|---|---|---|---|
| Hard water (above 7 gpg) | 90% | 79% | 60% |
| Iron above 0.3 mg/L | 40% | 35% | 19% |
| Manganese above 0.05 mg/L | 19% | 8% | 21% |
| Dissolved solids above 500 mg/L | 63% | 22% | 15% |
| Acidic water (pH below 6.5) | 25% | 15% | 14% |
| Nitrate above 10 mg/L (EPA limit) | Limited data | 2% | 4% |
| Arsenic above 10 µg/L (EPA limit) | 0% | 3% | 7% |
| Median hardness | 23.2 gpg | 12.4 gpg | — |
| Median pH | 7 | 7.2 | 7.3 |
St. Johns County and Florida: share of sampled wells (all well types, samples since 2000) whose typical value exceeds the level, from the Water Quality Portal. United States: USGS Circular 1332, about 2,100 domestic wells in 48 states sampled 1991 to 2004. Well types and years differ, so read this as a broad comparison. Highlighted cells are well above the national share.
See what a typical St. Johns County well needs
Opens the diagnostic calculator with St. Johns County median values (23.2 gpg hardness, 0.09 ppm iron, pH 7) for a 3–4 person home. Swap in your own lab results for an exact plan.
Testing Your Well in St. Johns County
The Florida Department of Health in St. Johns County supervises private water systems and publishes private well guidance for floods, including how to disinfect water if floodwater reaches your well. After any flooding, retest before drinking. For routine testing, use an FDOH-certified commercial lab.
For nitrates, metals, or a full panel, use a laboratory certified by the Florida Department of Health. The state’s private well water testing guide explains which tests to order and how to find a certified lab near you.
What to test for in St. Johns County:
- Bacteria (total coliform and E. coli) and nitrate, at least once a year (Florida Department of Health recommendation)
- Hardness in grains per gallon (gpg) to size a softener
- Chloride and sodium, to catch saltwater intrusion
- After any flood, new well work or a change in taste, color or smell
The Florida Department of Health in St. Johns County can explain how to collect samples and where to send them. Statewide guidance is on the FDOH private well testing page, and our guide to how to test well water covers which tests to order.
Nearby Counties
St. Johns County borders these counties with published reports:
Frequently Asked Questions
How hard is well water in St. Johns County?
Groundwater samples from 57 wells in St. Johns County have a median hardness of 23.2 grains per gallon (396 mg/L), which the USGS classes as very hard. About 90% of sampled wells are above 7 gpg, the point where a water softener is usually worthwhile. The Florida statewide median is 12.4 gpg.
Is iron a problem in St. Johns County well water?
The median iron level across 57 sampled wells is 0.09 mg/L, below the EPA aesthetic guideline of 0.3 mg/L, and 40% of wells exceed it. Most wells will not stain, but if yours does, a lab test tells you whether iron or manganese is the cause.
Why does my well water smell like rotten eggs in St. Johns County?
Hydrogen sulfide (the rotten-egg smell) was measured in only 0 St. Johns County wells, too few to say how common it is. Limited local data (fewer than 20 samples): individual well testing recommended. If you notice the smell, a sulfide test confirms it. The smell is a nuisance rather than a health risk at typical levels.
Which aquifer supplies wells in St. Johns County?
Most groundwater pumped in St. Johns County comes from the Floridan Aquifer (USGS, 2015 withdrawals).
Does boiling well water make it safe to drink in St. Johns County?
Only if bacteria are the problem. A one-minute rolling boil kills germs, but it does not remove nitrate, arsenic or other chemicals, and it concentrates them as water evaporates. Test first, and see our boiling well water myth buster for when boiling helps.
How many homes in St. Johns County use private wells?
The Florida Department of Health’s 2022 Florida Water Management Inventory found 9.7% of built parcels in St. Johns County on private wells, roughly 9,834 properties. Most of the county’s built parcels are served by public water systems; private wells are most common on rural lots and older properties outside utility service areas.
Where can I get my well water tested in St. Johns County?
Use an FDOH-certified commercial lab for routine tests. After any flooding, DOH-St. Johns recommends treating well water as unsafe until it is disinfected and retested; their private well flood guidance explains how.
Do I need to test my well water if my neighbors say theirs is fine?
Yes. Well depth, casing condition, and the exact aquifer layer tapped can vary block to block, so one neighbor’s clean test does not guarantee another’s. A full annual test is the only reliable way to know what is in your own water.
Is Floridan Aquifer water generally safe to drink untreated?
Much of it is chemically safe but aesthetically unpleasant (hard, sulfur-smelling, or iron-stained), which is why treatment here is usually about comfort and plumbing protection rather than an acute health risk. A lab test is still the only way to rule out bacteria, nitrates, or other contaminants specific to your well.
Written by Well Water Advisor Editorial Team.