Answer to Question #10155 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Radon

The following question was answered by an expert in the appropriate field:


I would like to test my private well water at my house. The laboratory has given me the option of testing it for radium, which is $275; radon, which is $100; or both. Is there one test that is better than the other?


The tests are different and one is not better than the other. Concentrations of radon and radium are not closely correlated, so the concentration of one is not a reliable indication of the concentration of the other.

There is very little risk from ingesting radon. However, radon transfers out of water into the air in a residence, adding to the indoor radon from other sources.1 If you are concerned about indoor radon, I would first test the air inside your residence. This can be done relatively inexpensively with a test kit obtained commercially or sometimes at reduced cost from a local public-health agency. If the indoor radon concentration is less than 4 picocuries per liter (pCi L-1 or 150 becquerels per cubic meter [Bq m-3]),* then you probably don’t need to be concerned about radon in water. If radon is higher than 4 pCi L-1 (150 Bq m-3)*, then the Environmental Protection Agency recommends that you take action to reduce it.2 At this point, you may wish to test your water for radon, especially if conventional methods of radon reduction are not completely effective.

Radium in water, on the other hand, delivers its radiation dose when ingested. If you want to know how much radium is in your well water, you will have to do the test.

One good reason for testing your well for radium would be the knowledge that your geographic area is prone to elevated radium in ground water. The most extensive region in the United States where radium-226 (226Ra) occurs in elevated concentrations in ground water is in the north-central states, including southern Minnesota, Wisconsin, northern Illinois, Iowa, and Missouri.3 High concentrations of 226Ra are also found in water derived from aquifers that straddle the fall line of the southeastern states from Georgia to New Jersey (this fall line runs approximately parallel to the Atlantic Coast and divides the eastern Atlantic Coastal plain, or tidewater, from the western Appalachian foothill region, or Piedmont).

More detailed information about geographic distributions of radium in water has been published for several states and regions, for example Southern New Jersey.4 You may be able to find this type of information for your area of residence with an internet search.

Another valid reason to test your water for radium is just because you want to know what it is for peace of mind.

Tom Gesell, PhD

*The radon concentration units are given here in pCi L-1 (called traditional units) because that is the unit used by the Environmental Protection Agency. However, the Health Physics Society has adopted SI (International System) units and these are given in brackets or parentheses.


  1. Risk Assessment of Radon in Drinking Water, National Academies Press; 1999.
  2. A Citizen's Guide to Radon
  3. Occurrence of Selected Radionuclides in Ground Water Used for Drinking Water in the United States: A Reconnaissance Survey, 1998
  4. Radium-226 and Radium-228 in Shallow Ground Water, Southern New Jersey
Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 29 March 2012. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.