In 2012, scientists of Riga Technical University have developed the regional hydrogeological model (HM) of Latvia (LAMO). LAMO covers 475km×300km area. It includes the territory of Latvia, the Gulf of Riga (active area of the HM) and border areas of the neighboring countries (presently, passive area of the HM). Both areas are separated by the border zone where outer boundary conditions for the active area must be fixed. LAMO simulates the steady state regime of the active groundwater zone that contains potable groundwater resources for Latvia. LAMO includes 25 geological layers and HM plane approximation step is 500 metres. The active LAMO volume is enveloped by its top and bottom surfaces, but the outer vertical surface of the border zone constitutes the shell of the HM. For the HM top and bottom surfaces and for the border zone, piezometric boundary conditions are arranged. Presence of the HM passive part makes the shell surface impermeable for the transboundary groundwater flow. This distortion of the natural groundwater regime must be compensated by a proper choice of boundary conditions that are fixed within the border zone. On the LAMO top surface, the digital relief (terrain) map is used as the boundary condition. The map includes elements of the hydrographical network (rivers, lakes, sea). The rivers are attached to various geological layers within the HM body. Special software has been developed to find the right attachment of over 200 rivers of Latvia to the HM. Lakes and the sea are joined with the HM through the aeration zone. The zone represents a formal aquitard that is considered in computing of infiltration flow for the HM. Because the digital relief is used as the boundary condition, the HM itself provides feasible infiltration flow distribution that can be adjusted by its calibration. Due to original methods of establishing the boundary conditions, LAMO has been created during a short period of time (2 years).