This paper demonstrates the use of computer-supported systems analysis in the derivation of least cost responses to municipally generated water pollution. In particular, a computer program is used to identify the least cost solution from a total system perspective by assembling all major treatment options and calculating their associated removal efficiencies and costs. The set of possible solutions consists of representative forms of industrial pretreatment together with the option to hook each major discharger to the municipal sewage treatment plant. In the example used in this paper, the optimization process identifies several alternatives that are less expensive than all industry hook-up with no pretreatment. The paper also briefly discusses the related issues of cost recovery and the economic efficiency of alternative effluent fee systems.