QMRA in the Drinking Water Distribution System

A Quantitative Microbial Risk Assessment (QMRA) model was developed for contamination events after mains repairs. The sensitivity analysis showed that the contamination concentration is the most important parameter, next to the pathogen dose response relation. The time of opening valves and of consumption are also important parameters. The event location within the network and the amount of consumption are of smaller importance. Issuing a boil water advice and opening only one valve before “releasing” the entire isolation section are effective measures to reduce the number of infected people per event by a factor of 2 to 4.