Optimal operation of pumping stations in Water Distribution Networks (WDNs) is presented based on three objectives, including 1) pumping energy costs, 2) hydraulic reliability (based on the nodal pressures and the velocity of water in the pipes), and 3) quality reliability (based on water age and the residual concentration of chlorine). We proposed a three objective optimization algorithm called Clustered Non-dominated Archiving Ant Colony Optimization (Clustered-NA-ACO) and evaluated the efficiency of this algorithm through seven DTLZ test functions. Incorporating k-means clustering strategy with NA-ACO can greatly improve the distribution of solutions and reduce the run time compared to NA-ACO. A pressure-driven analysis tool called EPANET-Iterative Modifications to Nodal Outflows (EPANET-IMNO) is developed for dynamic analysis of WDNs. In this research, the performance of WDNs is also evaluated from the perspective of transient flow. In this respect, the TRANSIENT code which is proposed by Larock et al. (1999) is revised and enhanced to handle the effects of the speed’s changes of the motor of V and . This TRANSIENT code and also EPANET-IMNO are linked to Clustered-NA-ACO to optimize the scheduling of pumping stations. We applied this simulation (EPANET-IMNO and TRANSIENT codes)-optimization tool to several WDNs. The results show the importance of considering transient flow in the optimization of WDNs. It is also concluded the necessity of evaluating the conflict of objective functions before combining them together. Key Words Water Distribution Network, Pump Scheduling, Multiobjective Optimization, EPANET-IMNO, Clustered-NA-ACO, Unsteady Flow, Reliability.
