Application of risk assessment tools to small drinking water systems in British Columbia

A number of risk assessment tools have been developed for drinking water systems, but there is a lack of published independent evaluation of how well the tools incorporate the multiple barrier approach to drinking water safety. Selected risk assessment tools were evaluated by applying the tools to five small drinking water systems serving residential developments in British Columbia. The selected risk assessment tools generally identified hazards and vulnerabilities in the source, distribution, storage and monitoring barriers of the water systems. The risk assessment tools had varying levels of success identifying vulnerabilities in the treatment barrier. In some cases, the existing tools consider the presence or absence of a water system barrier, such as a disinfection process or a monitoring procedure, but do not consider how effective or appropriate that barrier is. A common shortcoming of the risk assessment tools is the failure to identify the need for multiple treatment processes capable of removing or inactivating pathogens, which is particularly important for surface water supplies. In addition to not incorporating the multiple barrier approach into the evaluation of the treatment barrier, none of the risk assessment tools successfully reflected the interconnected nature of the water system barriers.