Water as Warning Medium: Food-Grade Dye Injection for Drinking Water Contamination Emergency Response

Once contamination of a drinking water distribution system is suspected or known, emergency managers may take different actions in response to the perceived state of the system. This study explores performance of a novel protective response action—injection of food-grade dye directly into drinking water—for minimization of health impacts as a contamination threat unfolds. Dye injection acts as an alerting mechanism that discourages public consumption of potentially contaminated water. Considering the uncertainties in threat observations and the imperfection in system understanding, however, the action has potential for costly false alarms. These could occur when contamination has indeed happened but population segments residing in safe regions are mistakenly alerted or when suspected indications of contamination occurrence turn out to be entirely wrong. The emergency response is, thus, formulated as a multiobjective optimization problem for the minimization of risks to life with minimum public warning and execution cost. Dye injection rates, locations, and timing are explicitly treated as optimization decision variables and sensitivity analyses are conducted on number of injection locations, response delay, and contamination scenario characteristics. Application to a virtual water distribution system demonstrates that dye injection holds potential as an effective contamination emergency response strategy. The results represented as a set of diverse nondominated alerting protocols provide valuable insight into optimal trade-off between achievement of health protection and avoidance of false alarms to public. The modeling framework can be useful for the management of contamination events for diverse types of contaminant agents without unintended damages to the system and interruption of firefighting.