Typical values from 2 sampled wells in Monroe County · Full groundwater profile
What Monroe County Wells Usually Need
Too little local data. Only a handful of Monroe County wells appear in public lab records, so your own test is the only reliable guide.
Is it safe? Local data is too thin to say, so test first.
Start with a certified lab test, then match equipment to the results. What to test for
Not sure what to install? Get a filter recommendation for Monroe County homesNot on a well? Tap water from a utility is covered by its yearly water quality report (CCR), not by these well samples. Find your utility's report
On this page (7 sections)
Where to Test Well Water in Monroe County
- DOH-Monroe's Environmental Public Health: 305-676-3941, 1100 Simonton St., Key West, FL 33040. Well testing details
- Certified labs: how to find a state-certified lab (FDOH)
Contacts as listed on the official page, checked November 2026. Call before you go; hours and fees change.
What Are You Noticing in Your Water?
Confirm with a lab test before buying equipment.
Explore Florida Interactive Map
Explore Monroe County and nearby counties
Monroe County, in the Florida Keys, is home to about 80,600 residents (2023 Census estimate). Here is what groundwater samples from local wells show, and how to test your own.
Most groundwater pumped in Monroe County comes from the Floridan Aquifer (USGS, 2015 withdrawals). Samples from 2 local wells put the median hardness at 285.2 gpg (very hard) and median iron at 0.3 mg/L. The county's largest communities are Key West, Key Largo and Marathon.
In this guide
Groundwater Profile: Monroe County
Most groundwater pumped in Monroe County comes from the Floridan Aquifer (USGS, 2015 withdrawals). Across 2 sampled wells, the median hardness is 285.2 gpg, which the USGS classes as very hard. It applies to wells across Monroe County, including around Key West, Marathon and Islamorada, Village of Islands.
Another address? Check hardness by ZIP code.
What shows up in local well samples:
- HardnessLimited local data (fewer than 20 samples): individual well testing recommended.
Calcium and magnesium dissolved from limestone. Leaves scale on fixtures and water heaters and reduces soap lather. Not a health risk.
Water softener sizing - IronLimited local data (fewer than 20 samples): individual well testing recommended.
Stains sinks, toilets and laundry orange-brown and can taste metallic. The EPA aesthetic guideline is 0.3 mg/L. See how to choose an iron filter for your test result.
Iron filter sizing guide - Chloride (salinity)Median chloride 14550 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 - SulfateMedian sulfate 2010 mg/L
A bitter taste and, at high levels, a laxative effect. The EPA aesthetic guideline is 250 mg/L.
Reverse osmosis guide
How Monroe County Compares to Florida and the U.S.
See How Monroe County Compares to Florida & the US
| Share of wells with… | Monroe CountyMonroe | FloridaFL | United StatesUS |
|---|---|---|---|
| Hard water (above 7 gpg) | Limited data | 79% | 60% |
| Iron above 0.3 mg/L | Limited data | 35% | 19% |
| Manganese above 0.05 mg/L | Limited data | 8% | 21% |
| Dissolved solids above 500 mg/L | 100% | 22% | 15% |
| Acidic water (pH below 6.5) | 0% | 15% | 14% |
| Nitrate above 10 mg/L (EPA limit) | No data | 2% | 4% |
| Arsenic above 10 µg/L (EPA limit) | Limited data | 3% | 7% |
| Median hardness | 285.2 gpg | 12.4 gpg | — |
| Median pH | 7.2 | 7.2 | 7.3 |
Sources: Water Quality Portal (since 2000); US: USGS Circular 1332. Highlighted: well above the US share.
See what a typical Monroe County well needs
Pre-filled with the Monroe medians. Swap in your own results.
Testing Your Well in Monroe County
The Florida Department of Health in Monroe County oversees private well permitting in the county and investigates suspected contamination. For routine bacteria, nitrate or full-panel tests, use a laboratory certified by the Florida Department of Health.
What to test for in Monroe 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
- Iron and manganese before choosing a filter
- Chloride and sodium, to catch saltwater intrusion
- After any flood, new well work or a change in taste, color or smell
Which tests to order and how: how to test well water.
After a positive coliform test, shock-chlorinate the well and retest 10 to 14 days later.
Nearby Counties
Monroe County borders these counties with published reports:
Frequently Asked Questions
Is well water in Monroe County safe to drink?
There is not enough local lab data to judge. A test for bacteria and nitrate is the minimum before drinking untreated water from a Monroe County well.
How hard is well water in Monroe County?
Groundwater samples from 2 wells in Monroe County have a median hardness of 285.2 grains per gallon (4877 mg/L), which the USGS classes as very hard. Limited local data (fewer than 20 samples): individual well testing recommended. The Florida statewide median is 12.4 gpg.
Is iron a problem in Monroe County well water?
The median iron level across 2 sampled wells is 0.3 mg/L, below the EPA aesthetic guideline of 0.3 mg/L (limited local data (fewer than 20 samples): individual well testing recommended). 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 Monroe County?
Public lab records include sulfide results for only 0 wells in Monroe, not enough to judge. The smell comes from hydrogen sulfide; a sulfide test confirms it, and at household levels it is a nuisance, not a health hazard.
Does boiling well water make it safe to drink in Monroe County?
Only against germs. A one-minute rolling boil kills bacteria after a positive test or a boil water notice, but it leaves minerals and chemicals behind in less water. See what boiling can and cannot fix.
How often should I test my well water in Monroe County?
The Florida Department of Health recommends testing private wells for bacteria and nitrate at least once a year, and again after flooding or well repairs. The Florida Department of Health in Monroe County can explain how to collect and submit samples.
Written by Well Water Advisor Editorial Team.