Chlorinated water has chlorine (a chemical) added to it. Chlorine disinfects the water and makes it suitable to drink.
Clean drinking water protects Canadians from illnesses caused by bacteria and other microbes in untreated water. These illnesses include cholera, giardiasis and sickness caused by the bacteria Escherichia coli (E.coli). E. coli can cause diarrhea, abdominal cramps and sometimes more serious illness.
Chlorine is a strong chemical, but the chlorine itself is not the main cause for concern in drinking water. When chlorine interacts with organic matter (such as dead leaves and soil) in untreated water, it forms new chemicals that remain in the water. These are called chlorination by-products. It is chlorination by-products that can increase cancer risk.
The amount of chlorination by-products formed during water treatment depends on the amount of chlorine used and on the amount of organic matter in the water.
How you are exposed to chlorine by-products
You’re exposed to chlorine by-products when you use water treated with chlorine. This includes drinking chlorinated water and breathing in water vapour during showering, swimming and other activities.
Chlorination by-products and cancer
The International Agency for Research on Cancer (IARC) classifies some chlorination by-products as possible causes of cancer. Find out more about how cancer-causing substances are classified.
For decades, researchers have studied the long-term effects of using chlorinated tap water. Most studies have shown that when people are exposed to chlorinated water over long periods of time, it slightly increases their risk of bladder cancer. Some studies have also found links to colorectal cancer, but we need more research to be sure of this link.
Several chlorination by-products are possible causes of cancer. Studies have shown that trihalomethanes (THMs) and haloacetic acids (HAAs), which are the most common chlorination by-products, can cause cancer in laboratory animals.
Many scientists believe that other chlorination by-products may also increase your risk of cancer. More research is needed about these and other chlorination by-products.
Tips to reduce your exposure
You may be able to reduce your exposure to chlorination by-products by:
- using activated carbon filter systems in your water pitcher
- attaching a filter to your tap
- using devices that filter all the water in your house
However, levels of chlorination by-products may not be reduced by all types of products mentioned here. And you can still be exposed to by-products when you shower or swim in a pool treated with chlorine.
If you choose to use these types of products, make sure they are certified to National Sanitation Foundation (NSF) standards. Also change the filters according to the manufacturer’s instructions to avoid contamination from bacteria and other microbes.
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