How Reliable are Water Distribution Networks?

Reliability analyses are performed on two large-scale water distribution systems in the Tucson Metropolitan Area in Arizona. Reliability is defined as the probability of satisfying nodal demands and pressure heads for various possible pipe failures (breaks) in the water distribution system. An existing reliability model based on a minimum cut-set method is linked to a steady-state simulation model that implicitly solves the continuity and energy equations. The results from the simulation model are used in the reliability model to define minimum cut sets and determine the values of system and nodal reliability. A discrete failure relationship is used with absolute failure if pressure heads fall below a prescribed minimum. Comparisons of results illustrate the similarities and differences in the design of each system under varying operating conditions. Design alternatives to improve reliability are discussed.