Comparison of solution methods for analyzing water distribution networks under pressure-deficient conditions Shokofeh Sharoonizadeh, Jafar Mamizadeh and Javad Sarvarian ABSTRACT Demand-driven analysis method is used in most current existing models for hydraulic evaluation of water supply networks. This method is based on the assumption of constant use, regardless of the available pressure in nodes. Demand-driven analysis method does not have sufficient efficiency in hydraulic analysis of networks under pressure-deficient conditions. In this study, the combination of pressure-deficient network algorithm (PDNA), modified pressure-deficient network algorithm (MPDNA), and complementary reservoir solution (CRS) methods with hydraulic model have been used to analyze series networks, looped networks, and a full-scale distribution network (part of the water network in Ilam city, Iran) in critical operating conditions. The critical condition in networks is created by breakage in a pipe network and fire-fighting demands on one node. Results showed that the required flow in networks has not been quite satisfied. The supplied outflow in the series, looped networks, and zone-6 network which used the three aforementioned methods are calculated as 76.40%, 90.25%, and 98.56% of total network demand, respectively. The results also showed that the number of required iterations to achieve the solutions in the PDNA method is more than in the MPDNA and CRS methods. Shokofeh Sharoonizadeh Jafar Mamizadeh (corresponding author) Javad Sarvarian Department of Water Engineering, Faculty of Agriculture, University of Ilam, Ilam, Iran E-mail: jafarmami@gmail.com Key words | artificial reservoir, pressure deficient, water distribution networks INTRODUCTION The process of providing high quality water and its transpor- tation to customers in semi-arid climates is one of the most important issues which experts are concerned with. Evaluating hydraulic networks and reducing water loss from both trans- mission and distribution lines may be regarded as a solution. Pressure in distribution systems should meet the minimum allowable limit in the maximum demand conditions. In other words, it should not cause bursting of pipes in the case of mini- mum demand on the network. Water distribution network (WDN) will be under pressure-deficient conditions if hydraulic or pressure heads in each node (consumer) are less than the required head. To resolve the pressure-deficient problem in a network, the first step is identifying areas with a low pressure. Therefore, we need to identify these points through simulation and resolve the pressure-deficient problem in an appropriate manner. Demand at pressure-deficient nodes could not be quite satisfied. Regardless of available pressure in nodes, most existing models for hydraulic analysis of water networks assume that demand is provided and simulate the network. This type of analysis is called demand-driven simulation method. Demand-driven methods, particularly under abnor- mal conditions in the network, such as pipe breakage, pipe failure, valve closure, or fire-fighting demand, would not pro- vide the required efficiency in hydraulic analysis of water distribution systems. Hence, it is necessary to consider the relationship between pressure and outflow in nodes to simulate 330 © IWA Publishing 2016 Journal of Water Supply: Research and Technology—AQUA | 65.4 | 2016 doi: 10.2166/aqua.2016.084