Designing roof catchment water supply systems using water budgeting methods

This paper describes the use of a water balance model to simulate the performance of a roof‐tank system over many years of historical rainfall data. Repeating this for a wide range of system specifications enables the construction of a set of design curves from which the most economic proportioning of roof and tank can be determined, for a nominated reliability of supply or a nominated cost. Two stations having identical mean annual rainfall but contrasting distributions are used as examples. Accuracy, problems of rainfall data availability, and practical aspects of computation are discussed.