Publications on Reservoir Induced Seismicity (RIS) in Spain are very scarce in spite of the remarkable importance that the problem can reach in the country. This communication describes its main characteristics and presents a computer program which calculates the incremental stress due to a water load (e.g. a reservoir). The program is based on Cough's methodology and assumes a two-dimensional geometry. An application to the Entrepehas reservoir area is also shown with the purpose of testing the usefulness of this program