Taquipe is one of the Petrobras operational bases for the oil exploration and production activities in Bahia. In order to develop its activities Taquipe uses large amounts of water, supplied through wells. The main consumption installations units are: garages, refectory and the drilling and completion fluid manufacturing plant (DCFMP). The aim of this article is to present a study about the use of rainwater as an alternative source for water supply in the DCFMP. The methodology used was divided into two stages. The first one was the construction of a hydric balance which was used to identify opportunities for optimising the water and effluent systems. The second stage was to conduct a study about one of these opportunities found: the use of rain water in the completion fluid manufacturing process. The amount of rain water available was determined by a hydrological study based in the precipitation historical registered in meteorological stations while its quality was found by a sample campaign. The samples were collected in points such as streets, gutters, canals and other drainage devices. The drainage basins inside the base and the runoff coefficients were also considered. The rain water quality was, then, compared to the water necessary for the completion fluid manufacturing process. Of the three drainage basins studied one was rejected because of the poor water quality. The critical parameters were Calcium, Bicarbonate and Hardness. A rain water system was designed, consisting of rain water reservoirs, pipelines and hydraulic pumps. This study represents a considerable advance in terms of the most modern principles about water resources. It will make possible to save 11344 cubic meters a year which represent 52% of water consumption in the completion fluid manufacturing process.