Radon in Water: Occurrence, Measurement and Treatment
Radon is a naturally occurring radioactive noble gas that can dissolve in groundwater. For well owners and water professionals, the key questions are whether radon is present in the water, whether it contributes to indoor air exposure, and which treatment approach is appropriate. This page complements the Radon.
Occurrence and properties
Radon forms through the radioactive decay of elements in rocks and soils. Its presence in groundwater depends partly on local geology and the water’s contact with those materials. Radon is colorless, odorless and chemically inert. Radon-222 has a half-life of approximately 3.823 days, so its activity decreases over time through radioactive decay.
Dissolved radon gas is distinct from dissolved radium ions. Radium in water may be a source of radon, but a radon measurement does not establish the radium concentration. Radon in water is commonly reported as activity in becquerels per liter (Bq/L), rather than as a mass concentration; one becquerel represents one radioactive decay per second.
Measurement and exposure pathways
Water sampling and laboratory analysis must account for radon’s ability to escape from water and its radioactive decay. Contact the testing laboratory before collection for its sample-container, handling and timing instructions, and provide the laboratory with the information it requests to interpret the result. A delayed or poorly handled sample may not represent the activity at the point of collection.
Radon can transfer from water to indoor air during household water use. Inhalation is the principal radon health concern, so evaluating a water result alongside an indoor air assessment provides a more useful picture of potential exposure. Radon entering a building from the ground can also affect indoor air; a water test alone cannot identify every source.
Treatment considerations
Aeration promotes transfer of dissolved radon from water into an air stream. Its design must account for discharge of that radon-bearing air outside occupied spaces. Granular activated carbon can also reduce radon in water by retaining it on the media, but radioactive material can accumulate in the carbon and requires appropriate management. Neither approach destroys radon; radioactive decay continues after it leaves the water.
Selection and assessment of treatment depend on the measured water activity, the indoor air findings and site conditions. There is no single treatment result or universal screening threshold applicable to every location. For a specific well or water system, discuss testing and treatment options with a qualified laboratory or water-treatment professional.
References
- World Health Organization: Radon and health.
- World Health Organization: WHO Handbook on Indoor Radon, water mitigation discussion.
- Royal Society of Chemistry: Radon element information.
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