Akbar Shirzad - Assistant Professor, Faculty of Civil Engineering, Urmia University of Technology, Urmia, Iran
Mehdi Dini - Assistant Professor, Civil Engineering Department, Azarbaijan Shahid Madani University, Tabriz, Iran
Massoud Tabesh - Professor, School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran

Reliability of water distribution networks is an important and interesting issue for researchers. In the previous researches, various indices have been introduced for evaluating the reliability of these networks. Reliability indices are either based on the demand driven analysis method or based on the pressure driven analysis method. Since the pressure driven analysis of water distribution networks has more realistic results than the demand driven analysis, in this paper a new index based on the pressure driven analysis method is considered. According to this index, nodal pressures are not the only most factors influencing the performance and reliability of the water distribution networks, but energy losses in pipes also affect the reliability of these networks. Ant colony optimization algorithm is used to maximize the network reliability. In the obtained optimal network, nodal pressures are near 35 m and energy losses are almost in the range of 1-5 m/km. The optimal network has high reliability. It means that the optimal WDN is able to satisfy the nodal demands in the normal operational conditions. In addition, in the abnormal (such as pipe breaks) operational conditions, a portion of the excessive pressure is consumed to compensate for the excessive energy loss and the pressure excess will decrease. Therefore, the optimal network would also be able to satisfy the nodal demands in the abnormal operational conditions.

Water distribution networks, Reliability, Ant colony optimization, Pressure driven analysis