Urban water distribution networks play a key role in the cycle of urban life. Networks have the responsibility of supplying water with appropriate quality, quantity and pressure at different times to consumers. These networks due to high length and also high administrative costs have been always considered by designers and managers of water resources and optimizing them economically and exploitationally over the past decade has been taken place. More studies on water distribution networks have the aim of optimizing the networks and minimizing the design costs and maximizing of mechanical or hydraulical reliability. This research has aimed to obtain a composite index of reliability by considering the mechanical, hydraulical and qualitative aspects and using it in sustainability indicator with the aim of increasing the sustainability of water distribution networks that means the ability of future generations to meet their needs and the introduction of composit index and sustainability index for using in future optimizations. composite index of reliability in this study using three indicators, the entropy for calculating mechanical reliability, resilience index for calculating the hydraulical reliability and water age index is used to calculate the qualitative reliability. Three indexes by interview with experts in water and wastewater organization of Isfahan and by the Saaty’s Multiple attribute decision making table defined as the composite index of reliability and repalaced as reliability index in order to complete sustainability index that is formed of three indexes of reliability, resiliency and vulnerability. In this thesis for water distribution network modeling has been used the EPANET software. Well-known examples of optimal water supply network in former studies, including two-loop network, NewYork, Anytown and Hanoi has been studied. The sustainability of these networks have been evaluated with new composite index of reliability and to improve the sustainability, each network has been changed randomly by considering the impact of water level in the reservoir to hydraulic behavior of the network and increase the number of tanks and pipes in the network’s pressure adjustment. In this research, a Two-loop network by changing the position of source was modified and sustainability index incresed from 0.51 to 0.63 that is in acceptable range. The sustainability index of the NewYork network by adding new source and loop incresed from 0.12 to 0.77 for indicating the pressure of 30 to 50 meters of water and 30 to 70 meters of water pressure indicating increased from 0.66 to 0.77 that is in acceptable range. for Hanoi network the sustainability index increased from 0.26 to 0.34 by adding new source. Systainability of the Anytown network was 0.45 and this network analyzed with different changes such as changing the position of source, adding new source and loop and,…but it’s first sustainability was at the highest level. The results show little change in the network such as changing the position of tank to the top node or adding a new source and pipe, reliability has been increased and also the network pressure adjusted and sustainability increased and at last the network will be able to respond better to needs. Researches show that spending the cost for design in order to increase the sustainability of water distribution networks can decrease the costs of modernization and improvement of the water distribution networks and network leakage -it’s about 30% of the total water entering the network-, and increased the composite reliability of network. Keywords : Reliability, Mechanical reliability, Hydraulical reliability, Qualitative reliability, Sustainability, Water age, Antropy, Resiliency, EPANET