The aim of this paper is to apply fuzzy/possibilistic optimization focus in the context of the water conservation in a petroleum industry. The idea is assessing the water requirements of the refining industry in the operational areas: topping, cracking, petrochemicals and lubes. The result showed that the raw water consumption is 25% and the reused water consumption is 75% approximately in refineries with daily crude capacities from 94 to 1500 bbls/day. (c) 2005 Elsevier B.V. All rights reserved.