Alterach Julio * , Peviani Maximo * , Vergata Milena *, Gervasio Ciaccia**, Fulvio Fontini***, Davitti Alessandro Giornale: Journal Hydropower & Dams Vol 5 2009 * ERSE SpA ** UNIVERSITA’ DI ROMA *** UNIVERISTA’ DI PADOVA The present paper describes the methodology to evaluate the residual potential hydropower energy taking into account the current water resource exploitation (irrigation, drinkable water, existing hydro power, etc). The model applied to the Italian territory uses a numerical technique coupled with a GIS, the hydrological and physiographic characteristics of nearly 1500 interconnected subbasins at a national scale and the rainfall maps information. The Italian maps of the water resources availability and the maximum potential hydropower are produced and illustrated. Finally the results of the residual potential hydropower for a case study are illustrated. These maps demonstrate to be quite helpful tools to support administrations, decision makers and stakeholders in general, to make Energy Master Plans, or assess and implement small scale hydropower plants. [*] This work has been financed by the Ministry of Economic Development with the Research Fund for the Italian Electrical System under the Contract Agreement established with the Ministry Decree of march 23, 2006.