Radon in Central Florida Well Water: EPA Data, Florida Groundwater Risk, and Treatment

Radon is a naturally occurring radioactive gas that forms as radium-226 decays in soil and rock. Florida's phosphate-rich geology elevates radium concentrations in the Floridan Aquifer system and the intermediate aquifer units that supply private wells across Lake, Marion, Alachua, Orange, and surrounding Central Florida counties. When groundwater contacts radium-bearing minerals in limestone and phosphate-bearing sediments, dissolved radon enters the water and travels to the tap. The U.S. Environmental Protection Agency proposed a maximum contaminant level of 300 picocuries per liter for radon in public water supplies in 1999, but that rule remains unfinalized. Private wells are exempt from federal oversight entirely. That regulatory gap means well owners in Central Florida have no mandatory testing requirement and often no way of knowing their radon levels without arranging a test. Laboratory testing from a Florida Department of Health certified lab establishes the baseline, and point-of-entry aeration systems can remove more than 95 percent of dissolved radon before water reaches any household fixture.

Does Central Florida well water contain radon?

Florida's phosphate geology and the Floridan Aquifer's limestone formations create conditions that elevate natural radon in groundwater across a wide area of the state. The central Florida phosphate mining district, spanning Polk, Hillsborough, Hardee, and Manatee counties, represents the highest-concentration zone in the state, but the geology producing elevated radium extends into Lake, Marion, Alachua, Citrus, and Orange counties as well. Radium concentrations in Floridan Aquifer rock are well above typical background values for limestone aquifer systems nationwide, and radon forms continuously from that radium decay throughout the aquifer.

The U.S. Geological Survey National Water Quality Assessment program has documented radon in Florida groundwater across multiple study periods. The Floridan Aquifer system, which underlies essentially all of peninsular Florida and supplies the majority of Central Florida private wells, draws water through limestone and dolomite formations containing uranium and radium at concentrations higher than much of the Southeast. Radon-222, the specific isotope of concern for drinking water, is produced continuously from radium-226 decay in the aquifer rock and enters groundwater through that ongoing process. The USGS National Water Information System at waterdata.usgs.gov/nwis includes historic radon measurements from Florida groundwater monitoring wells.

Private wells in Central Florida that draw from the Floridan Aquifer or the intermediate aquifer units above it are most likely to show detectable radon concentrations. Wells drawing from shallower surficial aquifer zones, where radium concentrations in the host sediments are generally lower and where dissolved radon has more opportunity to off-gas before reaching the pump, tend to show lower radon levels. Well depth and construction quality both affect what concentration arrives at your tap. A tightly sealed casing and a submersible pump in a deep Floridan Aquifer well can deliver dissolved radon at concentrations close to the aquifer equilibrium value, because the water has had little opportunity to lose radon through off-gassing during transit. Understanding whether your well draws from the Floridan or a shallower aquifer is relevant context for interpreting test results; our Lake County well water quality guide covers aquifer zones in detail for that county, and our karst county drilling guide explains aquifer structure across Marion, Alachua, and Citrus counties.

What is the EPA standard for radon in drinking water?

The EPA proposed a maximum contaminant level of 300 picocuries per liter for radon in community public water systems in November 1999. The agency simultaneously proposed an alternative maximum contaminant level of 4,000 picocuries per liter for water systems implementing an approved multimedia mitigation program that addresses radon in indoor air from all sources, not just water. The underlying logic is that a system taking broader action on the dominant radon pathway, indoor air from soil gas, need not reduce the water contribution as aggressively. The proposed rule, however, has not been finalized. As of 2026, no federal maximum contaminant level for radon in drinking water has been adopted under the Safe Drinking Water Act.

The health risk basis for the proposed 300 pCi/L level is lung cancer risk from radon that transfers from water into indoor air during showering, dishwashing, and laundry. The EPA estimated in the 1999 proposed rule that waterborne radon contributes to approximately 168 lung cancer deaths annually in the United States, with the inhalation pathway from water-to-air transfer accounting for the majority of that risk. The EPA's supporting materials for the proposed rule, including the health effects document, are indexed through the agency's radon in drinking water page at epa.gov/radiation/radon-drinking-water-health-risks.

Critically, even if the proposed MCL were finalized, it would apply only to community and non-transient non-community public water systems. Private wells are expressly outside the jurisdiction of the Safe Drinking Water Act. Florida has not adopted a state maximum contaminant level for radon in private well water. The absence of a mandatory standard does not reduce the health risk from elevated concentrations; it means the initiative to test and treat falls entirely on the well owner with no regulatory backstop. This is the same situation that applies to many contaminants in private wells, including nitrates, arsenic, and coliform bacteria, all of which we address in separate guides on this site.

How does radon get into Florida well water?

Radon-222 is the decay product of radium-226, which itself forms from the radioactive decay of uranium-238. Uranium occurs naturally in trace concentrations in most rocks and soils, but certain geologic formations concentrate it well above typical background levels. Florida's central phosphate belt contains phosphate rock with elevated uranium content, a well-documented association that was commercially exploited for uranium byproduct recovery at Florida phosphate processing plants for decades.

The Floridan Aquifer system, which supplies most Central Florida private wells, does not contain phosphate rock directly. However, it overlies or is laterally adjacent to phosphate-bearing formations across several Central Florida counties, and the aquifer limestone itself contains uranium and radium at concentrations sufficient to produce measurable radon dissolution into groundwater. Radium dissolved in groundwater decays to radon-222 with a half-life of 3.8 days. Because the travel time from deep aquifer rock to the well intake is typically weeks to months, radon produced by radium in the water itself, not only from the rock surface, adds to total dissolved radon concentrations reaching your well.

Closed well casings and properly positioned submersible pumps in deep Floridan Aquifer wells minimize the off-gassing that would otherwise reduce radon during transit. A well with a broken or deteriorated casing, or with a pump set relatively shallow within a deep well, allows more opportunity for dissolved radon to escape before reaching the pressure tank. Well construction and condition are therefore factors in what concentration actually arrives at your fixtures. If your well casing has not been inspected recently, reviewing its condition is worth combining with any water quality evaluation. For context on how well casing condition affects water quality more broadly, see our Florida well inspection guide.

Is radon in well water dangerous?

The EPA's health risk assessment concluded that the primary pathway of concern for radon in drinking water is inhalation, not ingestion. Radon dissolved in water releases into the air when water is agitated during showering, running a dishwasher, or doing laundry. This transferred radon contributes to indoor radon air concentrations, which carry an established lung cancer risk. The EPA estimated in the proposed rule's health effects analysis that the risk of lung cancer from lifetime ingestion of water at 300 pCi/L is roughly 1 in 1,000,000. The inhalation risk from water-to-air transfer at the same concentration is approximately ten times higher, around 1 in 100,000.

Radon in indoor air, regardless of its source, is the leading cause of lung cancer among non-smokers in the United States according to the EPA, accounting for approximately 21,000 deaths annually. The agency's indoor air radon action level is 4 picocuries per liter of air. A Central Florida well owner who has not tested either indoor air or well water has no baseline to determine whether either pathway represents a meaningful contributor to household cumulative radon exposure. In most Central Florida homes, soil gas is the dominant radon source, not water; however, where well water concentrations are elevated, the water contribution to indoor air can be meaningful during high-water-use periods.

The practical implication is that testing both indoor air and well water gives a more complete picture than either test alone. If indoor air is already near 4 pCi/L before accounting for any water contribution, addressing well water radon becomes a higher priority. If indoor air is very low, a modest water concentration contributes proportionally less to the total exposure picture. The Florida Department of Health offers radon information and guidance through its environmental health program at floridahealth.gov, including county-level data from the state's radon testing program.

How do I test my Florida private well for radon?

Laboratory testing is the only reliable way to determine radon concentrations in well water. The Florida Department of Health maintains a directory of laboratories certified for drinking water analysis, including radon, through its Environmental Laboratory Certification Program under Chapter 62-160 of the Florida Administrative Code. Certified laboratories can be located through the Florida DOH environmental laboratory program. A radon-specific water test is a separate order from a standard water quality panel and typically requires advance coordination with the lab.

Radon water testing requires specific sample collection procedures that differ from standard water quality sampling. Unlike a coliform or nitrate sample, a radon sample must be collected in a laboratory-supplied vial that limits off-gassing during storage and transport. Radon's 3.8-day half-life means that even modest delays between collection and analysis reduce measured concentrations. Same-week or overnight shipment is generally required for accurate results. The laboratory provides its collection instructions before you draw the sample; follow those instructions precisely, because improper collection is the most common cause of inaccurate radon water test results.

For a complete picture, conducting indoor air radon testing and water testing in the same period provides the most actionable data. Indoor air radon tests use passive charcoal canisters or electret ion chamber devices placed in the home for 48 hours to 90 days depending on the test type. The Florida DOH radon program lists state-certified measurement providers. Both tests together typically cost less than a minor plumbing service call and provide the basis for a defensible decision on whether treatment is warranted. Our Florida well water testing guide covers the broader panel of tests worth considering for Central Florida private wells, including parameters beyond radon that are more commonly tested.

What treatment removes radon from well water?

Point-of-entry aeration is the most effective and most commonly used treatment for radon in private well water. The EPA identified aeration as best available technology for radon removal in its 1999 proposed rule, with documented removal efficiencies above 95 percent for properly designed systems. Aeration works by exposing the well water to air in a controlled contact zone, which causes dissolved radon to transfer from the water phase to the air phase. The radon-bearing exhaust air is vented to the outdoors, and the treated water enters the household distribution system with a fraction of the original concentration.

Several aeration configurations are used in residential point-of-entry systems. Packed column aerators pass water through a tower of inert packing material while a fan draws outdoor air through the column in the countercurrent direction. Diffused bubble aerators inject air directly into a contact tank and collect the off-gas at the top for outdoor venting. Both designs require venting to the outdoors rather than to the interior of the house, which is a site consideration for installation. Adding a radon aerator system alongside existing water treatment equipment, such as an iron filter or whole house filtration system, is feasible in most installations and does not require replacing existing equipment. Our team can evaluate your existing system layout and determine the best integration point. For more context on whole house treatment system design, see our whole house well water filtration guide.

Granular activated carbon filters can reduce radon concentrations, typically achieving 70 to 90 percent removal at appropriate contact times, but they present a secondary issue worth understanding before selecting this approach. Carbon media accumulates radon and its short-lived decay products over time, and the filter canister becomes mildly radioactive as a result. Spent GAC media from radon applications requires specific handling and disposal procedures and is generally not suitable for normal residential solid waste disposal. Point-of-entry aeration avoids this issue entirely by transferring radon to the air stream rather than accumulating it in a filter medium. For most Central Florida well owners, aeration is the more practical long-term approach. The Water Quality Association publishes guidance on radon treatment selection through its consumer resources program for homeowners evaluating water treatment equipment purchases.

After any point-of-entry radon system is installed, a follow-up water test 30 to 60 days into operation confirms the system is achieving expected removal. System performance can change over time as aeration components age, so periodic retesting is a reasonable part of long-term maintenance. If your household water use has changed significantly, or if a system shows signs of reduced airflow or mechanical wear, a retest establishes whether treatment effectiveness has declined. Treatment equipment carrying NSF/ANSI certification for the specific performance claim has been tested by an independent laboratory against published standards and provides a more verifiable performance baseline than manufacturer specifications alone.

How does radon in well water compare to indoor air radon across Central Florida counties?

Central Florida does not rank among the highest-radon regions of the United States overall. Florida's flat topography and sandy soils result in lower average soil gas radon than granite-bedrock states like Pennsylvania, Colorado, or Minnesota, where building over certain geologic formations can produce indoor radon levels far above the 4 pCi/L action level without any water contribution. However, the Florida Department of Health's statewide radon testing program has documented meaningful variation by county and geologic zone, and some Central Florida counties show a higher proportion of tested homes above the EPA action level than the state median.

The groundwater pathway can be a material contributor to indoor air radon in Central Florida homes that rely on private wells, particularly in newer, well-sealed construction where natural ventilation is low and water is the dominant radon source competing with tightly controlled air exchange. An assessment that includes both air and water testing is the most complete approach for Central Florida well owners who want to understand their total radon exposure picture. The Florida DOH radon program provides statewide indoor radon data by county, which gives context for interpreting your own test results relative to the regional distribution.

For private well owners, water test results drive the treatment decision. Concentrations below 1,000 pCi/L in water combined with low indoor air radon suggest a modest combined exposure. Concentrations above 2,000 pCi/L in water represent a more material contribution to indoor air, particularly in homes with above-average water use or limited natural ventilation, and justify a consultation with a licensed water treatment professional to evaluate whether point-of-entry aeration is appropriate. This is the same pattern of test-first, treat-based-on-evidence approach we apply to every water quality parameter we work with, from iron and hydrogen sulfide to arsenic, nitrates, and PFAS. See our PFAS private wells guide, arsenic guide, and nitrate contamination guide for parallel treatment of those contaminants.