Trihalomethanes (THMs) are a group of chemicals that can contaminate drinking water. THMs are formed when the chlorine used to disinfect water reacts with natural organic matter (vegetation, dead leaves). THMs contamination occurs especially in drinking water systems supplied by surface water, such as lakes and rivers. THM concentration tends to increase in the summer and at the beginning of fall.
The standard for THM concentration in Québec is 80 micrograms/litre (80 µg/L). This is the annual average that should not be exceeded. Drinking water distribution system officials, including those of municipalities, are responsible for applying this standard.
You can be exposed to THM in running water these three ways:
Prolonged exposure (over a period of at least 20 years) to a high concentration of THMs in water could slightly increase the risk of bladder cancer.
If your municipal water utility officials inform you that THM levels in the water system are high, you should not necessarily stop using tap water. However, you can take preventive steps and reduce your exposure to THMs:
Even when water is contaminated with THMs, you can continue using tap water to:
You can prepare baby formula with tap water provided that you first bring the water to a rolling boil for at least 1 minute. The THMs will evaporate and any microbes will be destroyed.
Last update: November 25, 2016 11:19 AM
The information on this website by no means replaces the advice of a health professional. If you have questions regarding your health, contact Info-Santé 811 or see a health professional.