5 th International/11 th Construction Specialty Conference 5 e International/11 e Conférence spécialisée sur la construction Vancouver, British Columbia June 8 to June 10, 2015 / 8 juin au 10 juin 2015 RELIABILITY ANALYSIS OF WATER DISTRIBUTION NETWORKS USING MINIMUM CUT SET APPROACH Azhar Uddin Mohammed 1,3 , Tarek Zayed 1 , Osama Moselhi 1 and Alaa Alhawari 2 1 Building, Civil and Environmental Engineering, Concordia University, Canada 2 Department of Civil Engineering, Qatar University, Qatar 3 m_fnu@live.concordia.ca Abstract: Canadian Water and Wastewater Association (CWWA) estimated the cost to replace 112,000 km of water mains in Canada to be 34 billion Canadian Dollars. Reliability analysis of water distribution networks (WDNs) is an important aspect in planning and operation of a WDN and hence plays an important role in the efficient use of allocated budget. In general, reliability analysis is classified into mechanical reliability and hydraulic reliability. Mechanical reliability is defined as the ability to function even when some components are out of service or there is any mechanical break. Hydraulic reliability is concerned with delivery of the specified quantity of water to a specific location at the required time under the desired pressure. This paper introduces a methodology for evaluating mechanical reliability of WDNs using the minimum cut set approach. The methodology involves the computation of mechanical reliability at the component (pipe, hydrant etc.), segment (collection of pipes and components) and network levels. An illustrative example is worked out to demonstrate the use of the developed methodology. 1 INTRODUCTION Water distribution networks (WDN) are complex interconnected networks consisting of sources, pipes, and other hydraulic control elements such as pumps, valves, regulators, tanks etc., that require extensive planning and maintenance to ensure good quality water is delivered to all customers (Shinstine et al., 2002). These networks are often described in terms of a graph, with links representing the pipes, and nodes representing connections between pipes, hydraulic control elements, consumers, and sources (Ostfeld et al., 2002). They are vital part of urban infrastructure and require high investment, operation and maintenance costs. The main task of WDN is to provide consumers with a minimum acceptable level of supply (in terms of pressure, availability, and water quality) at all times under a range of operating conditions. The degree to which the network is able to achieve this, under both normal and abnormal conditions, is termed its reliability. (Atkinson et al., 2014). Hence, reliability is considered as an integral part in making decisions regarding the planning, design, and operation phases of WDNs. Many researchers defined reliability based on different conditions. Al-Zahrani and Syed (2005) defined reliability of WDN as its ability to deliver water to individual consumers in the required quantity and quality and under a satisfactory pressure head. Kalungi and Tanyimboh (2003) defined reliability as the extent to which the network can meet customer demands at adequate pressure under normal and abnormal operating conditions. In general reliability of any network refers to its ability of performing a mission placed on it, adequately under stated environmental conditions and for a prescribed time interval. No network is entirely reliable. In every network, undesirable events, i.e. failures, can cause decline or interruptions in the network performance (Ostfeld 2004). Reliability of WDNs relates to two types of failure, (1) mechanical failure of network components and (2) hydraulic failure caused by changes in