K.E. Lansey and L.W. Mays developed a new methodology for the minimum cost design of new and expansion of existing water distribution systems. This methodology interfaces a nonlinear programming optimizer with a hydraulic simulation model in which the simulator is used to solve the continuity and energy equation each time the optimizer needs these evaluated. The computer model is referred to as WADSOPT (WAter Distribution System OPTimization). The objective of this paper is to present a new feature of the Lansey and Mays model to consider the optimal rehabilitation and replacement in aging systems considering multiple loading conditions.