The dynamic constant of the volume of water in Reservoirs implies the need for continuous monitoring. Remote sensing in conjunction with geoprocessing and digital image processing are important tools in providing information that facilitates management and decision making in water resource management. The present work presents a methodology applied in images of the satellite Landsat 8, to verify the contribution of some image processing techniques, such as fusion and water index by normalized difference (NDWI), in the estimation of the volume of water in reservoirs. The study was carried out in the reservoir Engenheiro Francisco Saboia in the municipality of Ibimirim-PE, Brazil. The results were validated based on data provided by the Pernambuco Water and Climate Agency (APAC) and the National Water Agency (ANA). The methodology proved to be efficient in the monitoring of the volume of water in the reservoir, with the fusion of images and the NDWI a positive contribution in improving the accuracy of the results.