This paper describes a benefit/cost (B/C) model developed for the Regional Commission for Agricultural Development (CRDA) of the USAID-funded Rural Potable Water InstitutionsProject in Kasserine, Tunisia, in response to one of the principal objectives of the project: to maximize water investments by improving site selection for new and improved water systems. the model is used to allocate investment funds for rural water supply projects, according to a making of candidate sites based on the B/C criterion. It was developed byWASH and CRDA staff under a technical assistance program delivered under the WASH project.