This research aims to study the ability of using the technical methods of GIS in order to predict and calculate the capacity of restored water in front of dams, either under constructions, or already present. In this study, Al-Mojib Dam was chosen as a model for this research. The results obtained shows that GIS can be successfully be used to calculate the volumes of water accumulated in front of dams, and to calculate its capacity. It is concluded here that this application can be successfully applied for different dams in the Kingdom, to give an idea how to appoint water resources, and best location for dams to be constructed. Applying this techniques in Jordan, which suffering from water scarcity.