In Canada, we are very fortunate to have modern water treatment and distribution systems. Many good things have resulted from these systems, including the virtual eliminationof serious waterborne diseases such as cholera and typhoid in Canada. Our methods of water treatment and distribution have been described as among the major health-related advances of the past century.

But these benefits have not come without costs. In recent years, people have become increasingly concerned about negative effects that may result from our current drinking water treatment methods. There has been particular concern around the addition of chlorine to our water, as well as aluminum and fluoride. Studies have revealed that current chemical disinfection processes have the potential to create by-products that may be harmful to human health.

When weighing health benefits and risks, the use of such chemicals is still recommended by health authorities. Ideally the use of these chemicals is optimized, that is, treatment processes are adjusted to reduce quantities of needed chemicals as much as possible and yet still maintain the benefits of their use.

Fluoride

Fluoride has been found to make teeth more resistant to cavities, and for this reason began being added to Canada’s drinking water in the 1940’s and 1950’s to achieve dental benefits. Roughly 40% of Canadians receive drinking water that has fluoride added to it. In some children, exposure to low levels of fluoride can cause moderate to severe discolouration of the teeth, a condition called fluorosis, which affects the appearance of the teeth, but not their function. However, excessive intakes of fluoride can cause damage to tooth enamel, resulting in tooth pain and some problems with chewing. The risk goes away once teeth are formed, at age 6 or 7. Health Canada has set labelling requirements for dental products (such as toothpaste) that contain fluoride because young children have a tendency to swallow these products. For adults, high levels of fluorides consumed for a very long period of time may lead to skeletal fluorosis. Skeletal fluorosis is a progressive but not life-threatening disease in which bones increase in density and become more brittle. However, these levels are much higher than those to which the average Canadian is exposed daily, even with fluoridated drinking water. According to Health Canada, levels of fluoride in Canada are at least 20% lower than those associated with negative effects on the skeleton.

Chlorine

For more than 80 years chlorine has been the most commonly used disinfectant in water treatment. It is currently used in 98% of treatment plants in Canada. Chlorine is very effective at killing any bacteria found in source water, it offers the vadded benefit of remaining active in the water as it moves throughout the distribution system, thus providing ongoing protection from contamination even as the water flows from our taps. Chlorine also controls unpleasant tastes and odours in our water. In addition, it is relatively inexpensive to use.

However, when chlorine is added as a disinfectant to water with a high organic content, a number of other substances form as a result. Called "disinfection by-products," many of these substances have been discovered to be harmful to human health.These substances are created as a result of an interaction between chlorine added to the water and organic matter naturally present in the water, such as decayed vegetation and human and animal wastes.

Since a small amount of chlorine sometimes continues to be added to water at various intervals during distribution, the concentration of disinfection by-products may continue to increase until the water reaches our taps. Studies have shown that, from the time that water leaves the treatment plant to the time it reaches the consumer, the concentration of disinfection by-products may increase by 25 to 100%.To avoid this, many systems add ammonia to the system.

Among the most serious health risks associated with disinfection by-products are cancer and reproductive effects.  People who over a long period of time drink surface water that has been chlorinated and that contains high levels of disinfection by products, have an increased risk of developing bladder cancer and possibly colon cancer. Health Canada has identified chlorination by-products in drinking water as a moderately important public health problem and researchers are continuing to study the link between chlorinated tap water and cancer. Unfortunately the research to date on the links between disinfection by-products and health effects has not been extensive.

Adapted from Health Canada: Fluoride and Human Health and Drinking Water Chlorination, and Pollution Probe's Drinking Water Primer