Water utilities can prepare for water distribution iiazards, sucii as tiie presence of contaminants in the pipe networi< and faiiure of physical components, in contamination events, the compiex interactions among managers' operationai decisions, consumers' water consumption choices, and the hydrauiics and contaminant transport in the water distribution system may infiuence the contaminant piume so that a typicai engineering modei may not properiy predict pubiic heaith consequences. A compiex adaptive system (CAS) approach couples engineering modeis of a water distribution system with agent-based models of consumers and public officiais. Deveiopment of threat management strategies, which prescribe a set of actions to mitigate pubiic heaith consequences, is enabled through a simulation-optimization framework that coupies evoiutionary aigorithms with the CAS model. Evoiution strategies and genetic aigorithm-based approaches are deveioped and compared for an illustrative case study to identify a fiushing strategy for opening hydrants to minimize the number of exposed consumers and maintain acceptable levels of service in the networi<.