The Role of Scenario-Building in Risk Assessment and Decision-Making on Urban Water Reuse

Urban resilience and water resilience are both increasingly relying on urban non-potable water reuse under the context of the Climate Emergency, but sound risk assessment is lacking. Compared to the state of art, the proposed framework for health risk assessment and management of urban non-potable water reuse includes (i) an additional step for establishing the context and (ii) the risk identification step being extended to introduce a description of the activities from which the hazard exposure scenarios may be built. This novel scenario-building process allows for a clear and comprehensive risk description, assessment, and treatment. The model of risk management is structured around three primary components: the decision-makers, i.e., the municipal services and the population at risk (users and workers); data elements relevant for the risk management process (reclaimed water quality, hazards, hazardous events, sites where exposure can happen, exposure routes, and activities developed by the population at risk and their vulnerabilities); and the links between the decision-makers and these elements and between the elements themselves. Its application in a representative case study shows that the framework comprehensively guides decision-making and communication to relevant stakeholders. From this practical exercise, the main recommendations were derived for risk mitigation by the municipal risk manager and the park users.