This paper is concerned with the development of a computer-based graphics system for interactive simulation of pumping policies on water supply networks. The method evaluates various strategies which are input to the computer via a light-pen graphics facility, and displays to the operator the cost of the input strategy based on a mathematical model of the pumping tariff which is developed. The method has been used for policy analysis on a pressure zone of a network in the United Kingdom, and the calculations implemented on a Fortran-based minicomputer graphics system.