A model for the least cost layout and design of looped water distribution networks has been developed. The model consists of two linked linear programming formulations. One linear program determines the least cost layout of a looped distribution network given an initial pressure distribution. The other model determines the least cost component design given an initial flow pattern or pipe layout. The linkage between the two linear programs is provided by the use of output from one linear program as input to the other. Since the constraints in the layout model may provide looping without ensuring true redundancy in the system, a layout review is necessary after solutions of the layout model. If true redundancy is not present a set of ‘optional’ constraints can be applied and the layout model solved again. The procedure is demonstrated by application to a sample network.