Providing water to all the world's inhabitants is a daunting task. In order to make the task at all feasible, efficiency in planning is required. Demand-responsive project design is directly related to the sustainability of rural water systems, and cost recovery is a significant indicator of demand responsiveness. As such, cost recovery can be used as a proxy indicator of sustainability. Here, a cost recovery criterion is developed using fuzzy set theory as an uncertainty representation tool. This criterion is based on the Hamming distance measure and allows for the quantitative distinction between costs and revenues. Such a tool has utility in the comparison of alternative projects and policies for sustainable project selection. (c) 2004 Elsevier Ltd. All rights reserved.