The high cost of pipe repair and replacement and the importance of the hydraulic performance in water distribution networks have faced the management of these networks with serious management challenges. The solution to these challenges is providing an optimal instruction of pipes repair and replacement with minimum cost and maximum hydraulic performance, which is the principal purpose of this research. A new hydraulic performance index was developed, considering the demand deficit of nodes. The proposed approach of this research is a combination of a hydraulic simulation model, a hybrid prediction model of pipes failure rate, a multi-objective optimization model, and a voting multi-criteria decision-making model. The approach is used in part of Gorgan's water distribution network. Implementing the optimal instruction of pipe repair and replacement improves the quality of pipes (70% reduction in pipe failure rate) and increases the nodes' average pressure and network reliability index by 94.3% and 52.64%, respectively.
