The water balances of watersheds are a fundamental tool in the field of water resources planning. In the global context, a water balance, at the level of a river basin, consists in correlating the runoff of the basin (supply) with the consumptive and non-consumptive demands, there by determining the existing excess / deficit, which is the base For the establishment of plans for optimal control and use of water resources.Based on the SCS methodology, the runoff of the 56 micro-basins of Hydrographic Demarcation the Manabi (Ecuador) (HDM) has been calculated, followed by the demands contemplated in the Integral Plan for the Development of Water Resources 1990, updated to the year 2013, was estimated the respective excess / deficit.