A critical review of risk matrices used in water safety planning: improving risk matrix construction

Abstract

Risk matricesãre used in water safety planning to prioritize improvements to drinking water systems. While water safety plans (WSPs)ãre promoted globally, no study has evaluated whether risk matricesãre comprehensively constructed toãccuratelyãssess risk. We used risk matrix criteriaãdapted from previous risk matrix research to evaluate risk matrices found in twelve templatesãcross global jurisdictions. WSP templates were found using the WSPortal websiteãnd definitions of likelihoodãnd impact were extracted from each template toãssist in the evaluation of WSP risk matrices. Application of the criteria developed fromã detailed mathematicalãnalysis by revealed that 11 of 12 risk matrices evaluated contraveneãt least one of the risk matrix criteria. Furthermore, definitions of likelihoodãnd impact varied widelyãcross different jurisdictions, due in part to the system specific nature of the WSP methodology. To improve risk matrix construction, we recommend: setting clearer risk level boundary criteria,ãligning specific impact category definitions with water system objectives,ãnd selecting specific impact categoriesãs opposed to defining impact in several ways. Finally, we recommend risk matrix construction be reviewedãs part of the WSP process to ensureãccurate identification of key risks inã water system.