Evaluation of Risk Assessment Tools to Predict Canadian Waterborne Disease Outbreaks

A number of risk assessment tools and guidance documents have been developed by regulatory and nongovernmental bodies to enable risk assessment of drinking water systems. To evaluate the strengths and weaknesses of available risk assessment tools, three of the existing risk assessment tools were applied to waterborne disease outbreaks in North Battleford, Saskatchewan, and Walkerton, Ontario, to determine whether the risk assessment tools would have indicated that the water systems were at risk of failure. Both of these outbreaks are sufficiently well documented to allow testing of the risk assessment tools. Both of the outbreaks occurred partly due to vulnerabilities that prevented the respective water systems from having effective multiple barriers to drinking water contamination. The risk assessment tools generally identified the hazards that resulted in contamination of the source water. However, the different tools had different levels of success in identifying vulnerabilities in the downstream barriers such as treatment processes and water quality monitoring activities. None of the risk assessment tools successfully incorporated the interdependent nature of the multiple barriers of drinking water safety.