Drinking Water Chlorination By Health Canada
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Drinking Water Chlorination By Health Canada

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The risks of chlorination by-products lab animals exposed to very high levels of THMS have an increased risk of cancer. Several studies on humans have also found a link between long-term exposures to ...

The risks of chlorination by-products lab animals exposed to very high levels of THMS have an increased risk of cancer. Several studies on humans have also found a link between long-term exposures to high levels of chlorination by-products and a higher risk of cancer. For instance, a recent study showed an increased risk of bladder and possibly colon cancer in people who drank chlorinated water for 35 years or more.

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Drinking Water Chlorination By Health Canada Document Transcript

  • 1. Health Canada Santé Canada It’s Your Health DRINKING WATER CHLORINATION The Issue rine is needed to disinfect at colder tem- peratures. THM levels are also low Chlorine is a disinfectant added to drink- when wells or large lakes are the drink- ing water to reduce or eliminate microor- ing water source, and higher when rivers ganisms, such as bacteria and viruses, or other surface waters are the source, which can be present in water supplies. because they generally contain more The addition of chlorine to our drinking organic matter. water has greatly reduced the risk of waterborne diseases. The Benefits of Chlorine Background Current scientific data shows that the benefits of chlorinating our drinking For more than a century, the safety of water (less disease) are much greater Canadian drinking water supplies has than any health risks from THMs and been greatly improved by the addition of other by-products. Although other disin- chlorine. Disinfecting our drinking water fectants are available, chlorine remains ensures it is free of the microorganisms the choice of water treatment experts. that can cause serious and life-threaten- When used with modern water filtration ing diseases, such as cholera and methods, chlorine is effective against vir- typhoid fever. To this day, chlorine tually all microorganisms. Chlorine is remains the most commonly used drink- easy to apply and small amounts of the ing water disinfectant, and the disinfec- chemical remain in the water as it travels tant for which we have the most scientific in the distribution system from the treat- information. ment plant to the consumer’s tap,This level of effectiveness ensures that Chlorine is added as part of the drinking microorganisms cannot recontaminate water treatment process. However, chlo- the water after it leaves the treatment rine also reacts with the organic matter, plant. naturally present in water, such as decaying leaves. This chemical reaction forms a group of chemicals known as Alternatives to disinfection by-products. The most com- mon of these by-products are tri- Chlorination halomethanes (THMs), which include A number of cities use ozone to disinfect chloroform. The amount of THMs found their water, because ozonation does not in drinking water depends on a number produce THMs. Although ozone is a very of things, including the season and the effective disinfectant, it breaks down source of the water. For example, THM quickly and cannot be used to maintain levels are generally lower in winter than disinfection in the distribution system. in summer, because the amount of natu- ral organic matter is lower and less chlo-
  • 2. Small amounts of chlorine or other disinfectants still must be High levels of THMs may also have an effect on pregnancy. A Minimizing Your added. Renovating water treat- California study found that preg- Risk ment plants so they can use nant women who drank large ozone can be expensive. amounts of tap water with high Drinking water that meets the THMs had an increased risk of guidelines does not usually need Examples of other disinfectants miscarriage. These studies do extra treatment. There is no easy include chloramines and chlorine not prove that there is a link way that you can remove all dis- dioxide. Chloramines are weaker between THMs and cancer or infection by-products, but here disinfectants than chlorine, but miscarriage. However, they do are some steps you can take. are very effective in the distribu- show the need for further tion system. Chlorine dioxide can • Activated carbon filters can research in this area to confirm be used in the treatment plant, be used to remove chlorine potential health effects. but it is not very effective in the and its by-products. If you distribution system . choose to use such a filter, it How the is essential to follow the man- All chemical disinfectants used in ufacturer’s instruction drinking water can be expected Government Protects to form by-products that could • The manufacture and sale of affect human health. In general, Your Water Supply water treatment devices are we know less about the by-prod- not regulated in Canada. The federal and provincial gov- ucts of other disinfectants than Health Canada recommends ernments share responsibility for about chlorination by-products. the use of products that are safe drinking water. Provincial certified to health-based stan- governments are generally dards. The Standards Council responsible for the day-to-day The Risks of provision of drinking water to their of Canada can provide infor- mation on the certification Chlorination By- constituents. The water they pro- process. vide must meet their own drinking Products water requirements, which are Lab animals exposed to very based on the Guidelines for Canadian Drinking Water Quality. Need More Info? high levels of THMs have an These guidelines are published For more information on drinking increased risk of cancer. Several by Health Canada and developed water quality issues in Canada, studies on humans have also in collaboration with all provincial please visit Health Canada’s found a link between long-term and territorial governments. Water Quality Activities Web Site exposure to high levels of chlori- Health Canada publishes an at www.hc-sc.gc.ca/waterquality nation by-products and a higher annual table summary of the risk of cancer. For instance, a guidelines, which is available on recent study showed an its Web Site. increased risk of bladder and possibly colon cancer in people Health Canada has established a who drank chlorinated water for guideline for THMs of 0.1 mil- 35 years or more. ligrams per litre. The cancer risk at this level over a lifetime is con- sidered extremely low. The guide- lines for THMs and other chlori- nation by-products are currently under review by a task group whose work is coordinated by Health Canada.