Choice of Reliability Indicator for Service Assessment of Water Distribution System

Performance assessment of WDS has been extensively reported in the research and practice literature. The use of performance indicators (PIs) can play a key role in the process of measuring the quality of service provided by the water utility, can simplify the comparison between different objectives, and help decision processes involved in the planning and management phases. The use of PIs like reliability, resiliency and vulnerability have been approved by many authors and researchers, and led to the achievement of wide numbers of research studies in multidisciplinary scientific fields (Hashimoto et al., 1982; Fiering, 1982a; Merabtene et al., 2002). In reality, in WDS, different kinds of failure like that related to pressure, flow and water quality are linked with similar or same parameters. As a results, when one kind of failure occurred it also influences the other type of failure. Therefore, consideration of holistic system performance with regards to various aspects will make the process more complicated but decision makers will potentially gain insights into the performance of the whole system as well as the information on the impacts of each component and aspect on improving the overall performance. The proposed methodology is based on a hierarchical system approach that begins by identifying two aspects namely; hydraulic and water quality aspects, which could be divided broadly into available nodal pressure and available flow, and available free residual chlorine concentration, respectively. Then, based on these services, three complementary reliability estimators (index) are adopted namely; demand-reliability, pressure-reliability, and quality-reliability. To reach the outcome of the proposed approach which is the overall reliability, analytical hierarchy process (AHP) coupled with fuzzy theory is then developed to bring all the reliability estimators into a unique platform and aggregate them into one index. The final model outcome is a single index that depicts the overall reliability which resembles both the hydraulic and water quality performances, and provides a comprehensive evaluation of the system.