Hydrogeologists are interested in borders that separate the groundwater recharge, transit, discharge (RTD) areas. Unfortunately, no good method exists for finding them. In the course of using the hydrogeological model (HM) of Latvia (LAMO) scientists of Riga Technical University have developed the new method that generalizes the RTD concept and gives locations of the borders. LAMO is run by the commercial program Groundwater Vistas (GV). The GV program provides the velocities vz for the vertical and vx, vy for the horizontal groundwater flows. These velocities are used to create the function r for describing the borderlines of the RTD areas. The function r originates the four areas: R, positive T (+T), negative T ( T), D. The value r = 0 denotes the border that separates the +T and –T areas. The values r = 1; r = -1 depict the borders between the R, and +T; -T and D areas, correspondingly. The new method will be applied for investigating the regional groundwater processes that are modelled by LAMO