What is Radon?

Radon is a radioactive gas produced naturally by the decay of uranium in the earth’s crust. It exists all over the world, although its production and, consequently, its concentration are not uniform. When radon is released from the ground into the outdoor air, it gets diluted to low concentrations and is not a concern.

Radon concentration in water is also highly variable. Drinking water can be obtained from groundwater sources such as springs, wells and boreholes. Groundwater often flows through rock formations which contain natural uranium and radon producing radium. As radon is a water soluble gas, these sources of water normally have much higher concentrations of radon than surface water from rivers, lakes and streams.

When radon infiltrates an enclosed space, like a house, it can sometimes accumulate to high levels, which can be a risk to the health of you and your family. Because radon is odourless, colourless and tasteless, it cannot be detected by the senses.

Whether your house is new or old, radon tends to accumulate in the lower and less ventilated rooms, like the basement for example. The gas can seep into the house in a variety of places. The only way to know if you have a radon problem in your home is to measure its concentration.

Health Impacts

The only known risk is long-term development of lung cancer. The level of risk depends on the concentration of radon as well as the number of years of exposure. It is estimated that 10% of all lung-cancer-related deaths in Quebec are linked to radon exposure. Smokers run a much greater risk than non-smokers (including second-hand smoke). In fact, individuals who are exposed to both tobacco smoke and high levels of radon over an extended period of time are more likely to develop lung cancer. The effect is more than additive. Incidentally, 60% of radon-related lung cancer deaths occur among smokers while 30% occur among former smokers. For example, if you smoke your entire life and are exposed to 800 Bq/m3 of radon, your risk of developing cancer is 1 in 3. To date, epidemiological studies have not found an association between radon in drinking water and cancer of the digestive and other systems.

Testing for radon

The only way to know if you have a radon problem in your home is to measure its levels. The marketplace offers a number of measuring devices and services. Testing is safe, simple and relatively inexpensive (approximately $50). Various devices allow you to measure radon concentrations over short periods while others do so over several months. Health Canada recommends measuring radon in your home for at least three (3) months, ideally in winter. The test must be performed in a room occupied more than four (4) hours a day and located on the lowest level, e.g. basement bedroom or recreation room. If the annual average exceeds 200 becquerels per cubic meter of air (200Bq/m3 ), corrective measures should be taken. (A becquerel is a unit of radioactivity equal to one disintegration per second).


The best time to measure radon in your home is from October to March because windows are generally closed and radon concentrations tend to increase inside buildings.

Recommendation* for measurement of radon in air and well water in Chelsea

If your house uses water from a well, like the majority of homes in Chelsea, it is recommended to test for radon in air on each inhabited level of your house.

Why? Radon is a gas that gets dissolved in water. If your well water is rich in radon because it is in contact with bedrock which is itself rich in radon, the water used for domestic activities (e.g. laundry, dishwasher, shower) contributes to radon in air. The microscopic bubbles of radon contained in groundwater degas when water is agitated and/or heated, and end up in the air.

Step 1:

Test for radon in air on each level of your house where a person spends in average at least 4 hours per day. Use long-term measurement devices (min. 3 months) during the heating season, as recommended by Health Canada.

Step 2: If you get a result in air that is higher than Health Canada’s guideline (200 Bq/m3), consider testing your well water. This helps to determine if your well water contributes to radon in air in your house, in which case mitigation measures on your well would be appropriate.

*Measurement recommendation developed jointly by the Planning and Sustainable Development Services of the Municipality of Chelsea, Health Canada, and the Public Health Department of the CISSS de l’Outaouais, nov. 2015.

 Where Can I Buy a Radon Detection Kit?

It is recommended to test your house for radon in the air first. If you do have radon in the air, you can then test the water to verify the origin of the radon in your house. A part can come from your well water or your foundation or both. 

RADON AIR KITS (long term 90 days test period)


  • Town Hall, Municipality of Chelsea*:  $65

*The kit includes a single device, one heat pad to avoid any freezing during transit, a pre-paid return envelope, instructions and laboratory analysis.  Once you have collected your water sample, you have to send back the dosimeter to the laboratory.  The vial must reach the laboratory within 48 hours of the water collection, otherwise the test becomes invalid.  A pre-paid return shipping label and envelope is included in the kit so you won't have to worry about transit time.  You have to bring back the envelope to a FEDEX deposit point before closing time on the same day of your water testing.  To find the nearest FEDEX deposit point click here.

Radon: A Guide for Canadian Homeowners

This comprehensive guide explains everything you need to know about radon : Radon: A Guide for Canadian Homeowners
 Additional information


The information contained in this document was adapted from documents published by the following organisations : Health Canada, the Québec Lung Association, the Ministère de la Santé et des Services Sociaux du Québec, the Canada Mortgage and Housing Corporation and the World Health Organisation.