In this paper the hydraulic performance of water distribution networks is evaluated by assessing the head values in demand points and velocities in pipes. To obtain the hydraulic parameters a head-driven simulation method is used. In this method, nodal outflows are not fixed and vary with nodal heads. Considering the possibility of a range of demand variations and mechanical and hydraulic failures in the system, nodal heads and pressure dependent outflows are obtained. Then, by using a mathematical function, the performance of the system is realistically evaluated. As expected, the level of service in the system is decreased when head and velocity values are out of the standard ranges. Also, the reliability of a water distribution network is calculated using the ratio of the pressure-dependent outflows to the demand values considering the probability of pipe failures. Comparing the level of service index and reliability applications on a test network, it can be concluded that the reliability method is not sensitive to high-pressure values in the system. However, in this situation the performance index shows a lower level of service in the network. This means that high reliability values guarantee a good connectivity and enough pressure to satisfy the required nodal outflows, although pressure values higher than the standard codes, which lead to more leaks and bursts, are not acceptable in water supply systems. Therefore, the existing definitions of reliability are not comprehensive enough to realistically evaluate performance of the system. Using the level of service index and the head-driven simulation method, the network performance under different normal and abnormal conditions can be appropriately evaluated for water companies.

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