19. Chlorination of Drinking Water – Scientific Evidence and Policy Implications

Identification of the value of chlorine as an efficient oxidant and disinfectant resulted in its subsequent worldwide application for disinfecting water, and is considered one of most important discoveries of the early twentieth century, improving public health. The use of chlorine in various forms continued at worldwide scale, for subsequent decades, until the 1970s when it was identified that chlorine reacts with naturally occurring organic compounds, producing potentially harmful disinfection byproducts (DBPs). Regardless, despite widespread concerns around DBPs and the inclusion in drinking water guidelines and regulations for some DBPs, many communities (especially small and rural communities with limited resources) rely solely on chlorine as primary disinfectant. Also, the use of chlorine as a secondary disinfectant to ensure residual disinfectant in the distribution system is required in many parts of the world, including in Canada. Public resentment to having chlorine in their water is a challenge associated with the use of this disinfectant in drinking water supplies, especially in aboriginal communities, with many disliking the taste and odour of chlorine, making the policy around chlorination of water very difficult and complicated. While science supports the benefits of maintaining residual chlorine in water supplies, it warns of DBP formation and its potential impact to public health. Hence, resistance to implementation of policy due to public perception and resentment continues. The work presented will describe the role of science in shaping the policy and public opinion around the use of chlorine in drinking water supplies, with particular emphasis on small and rural communities.