On the significance of maximum number of components failures in reliability analysis of water distribution systems

Many factors may influence the results of a reliability analysis for a water distribution system (WDS). These may include (but not limited to) the techniques chosen for reliability assessment, criterion to measure a system's reliability, number of components-failure combinations and failure probabilities and/or frequencies. Among these factors, the maximum number of components-failure scenarios is an important one which has not received sufficient attention in the literature. This study estimated the accuracy in reliability and damage tolerance analysis when an unrealistic and imprecise number of failure scenarios is assumed. Exercising a hypothetical WDS, the modified version of EPANET2 was applied for the hydraulic analysis. The reliability and redundancy or damage tolerance were evaluated based on weighted mean of performance indices of the system. The results indicated that incorporation of maximum acceptable error allow the engineers to estimate the number of failure combinations and ultimately to conduct a more computationally-efficient and realistic reliability assessment. Application of this methodology prevents redundant and unnecessary hydraulic simulations in reliability analysis and reduces computational simulations significantly.