This paper presents a methodology to assess and reduce water residence times in a water distribution system in order to improve water quality. The methodology was developed and validated on Quebec City's main distribution system. A tracer study was conducted to evaluate real residence times and results are presented in the ‘companion paper’ (Part I) in this issue. A hydraulic model was then built to simulate the mean residence times (MRT) and develop strategies to reduce them. An optimization algorithm (hybrid discrete dynamically dimensioned search, HD-DDS) was used to calibrate the model using flows and pressures measured in the distribution system. Results show that the suggested methodology can lead to significant reductions in MRT (25.6%) in parts of the distribution system, but could also lead to significant loss in pressure, which should be monitored closely.

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