Arsenic is widespread in Miami-Dade County wells.
1 widespread, 1 worth checking, 5 rare out of 7 health checks.
From 171 wells tested in Miami-Dade County since 2002; your own well needs its own test. How to read this
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
About 1 in 59 people 46,032 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
Radon risk (a gas from rock)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how Miami-Dade County compares with Florida and the counties around it.
Each result puts Miami-Dade County next to the 3 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Miami-Dade County wells.
Arsenic18 of 114 wells over
Too few tested to show: Monroe.
This one is worth checking in Miami-Dade County.
Lead7 of 87 wells over
Too few tested to show: Monroe.
These 5 are rare in Miami-Dade County.
Manganese1 of 142 wells over
Too few tested to show: Monroe.
Nitrate0 of 103 wells over
Too few tested to show: Monroe.
Radon in water0 of 17 wells over
Too few tested to show: Collier, Monroe.
Fluoride0 of 148 wells over
Too few tested to show: Monroe.
Uranium0 of 88 wells over
Too few tested to show: Monroe.
Coliform bacteria turned up in 42 of 70 tested Miami-Dade County wells, so test for it every year.
Coliform bacteria42 of 70 wells had it
Too few tested to show: Monroe.
Most of Florida's bacteria results come from shallow monitoring-network wells, so they aren't a guide to household wells.
E. coli14 of 54 wells had it
Too few tested to show: Monroe.
E. coli means human or animal waste is getting in, so if a test of your Miami-Dade County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 99 of 154 tested wells, and it isn't a health risk.
Iron stains99 of 154 wells had it
Too few tested to show: Monroe.
Miami-Dade County has 171 tested wells, and the busiest decade for testing was the 2010s.
Only 45 of the 171 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Miami-Dade County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 4 things to check in Miami-Dade County.
- Bacteria
- Nitrate
- Arsenic
- Lead
What Florida offers well owners
- Free testingSome county health departments may test for certain toxic substances free of charge. See the program
- Certified labsFlorida's list of certified labs
- Well recordsWe didn't find an online search.
- New wellsNo statewide rule. We didn't find a local rule for Miami-Dade County, so ask its health department.
Here's what we know about radon and PFAS in Miami-Dade County.
Miami-Dade County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide
Between 2023 and 2025 the EPA had 17 town water systems in Miami-Dade County test for PFAS. 17 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 50 ng/L of PFOS. No well in Miami-Dade County has public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Miami-Dade County
Is well water in Miami-Dade County safe to drink?
18 of 114 wells tested in Miami-Dade County had arsenic over the limit, about 2 in 10. Across Florida it's about 1 in 9. That's a bigger share than in 50 of the 63 other Florida counties with 10 or more tested wells. So test your own well for arsenic before you count on it.
Can I get my well tested for free in Miami-Dade County?
Some county health departments may test for certain toxic substances free of charge. If not, use a lab Florida has certified for drinking water. Ask for bacteria, nitrate, arsenic and lead, the tests that matter most in Miami-Dade County.
How does Miami-Dade County compare with the counties around it?
For arsenic, the share of tested wells over the limit: Miami-Dade County, at 16%, had a higher share than all 2 neighboring counties with data. Groundwater doesn't stop at county lines, so Collier's 8% is worth knowing about if you live near it.
How often should I test my well in Miami-Dade County?
In Miami-Dade County, 42 of 70 tested wells had coliform bacteria, so the CDC's advice matters here: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the Miami-Dade County numbers come from
- People on wells: 46,032 in Miami-Dade County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 1,916 well water samples from 171 wells in the Water Quality Portal, run by the USGS and EPA, 2002 to 2026.
- Neighboring counties: the 3 counties that share a border with Miami-Dade County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 17 town water systems in Miami-Dade County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Miami-Dade County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: Department of Health, checked November 1, 2026.