This study was conducted in the “Paramo and High Andean Forest System of the Middle Northwest of Antioquia” Special Management Area (SMA), located in the Department of Antioquia, Colombia . The SMA has a total extension of 34.358,74 ha. The main object of this investigation was to estimate the environmental supply of hydric resource that originate in this system and with secondary objectives the estimation of monthly and annual average originate in the system, as well as to estimate the annual minimal volume for different periods of return. To achieve these objectives the “water accounting procedure to accomplish a detailed water balance according to Holdridge” and the regionalization of the mean characteristics method were used. As results for the SMA, a precipitation of 665.288.946,00 m3·year- 1, a real evapo-transpiration of 242.363.796,00 m3·year-1 and an annual run-off average of 422.925.149,57 m3·year- 1. A run-off coefficient of 63,6% was obtained, which signifies that 63,6% of the precipitation becomes run-off and the 36,4% remainder is lost by evapotranspiration. As conclusion the study area has an annual precipitation mean, ( 1.847,4 mm), that is less than the annual precipitation average for Colombia ( 3.000 mm) and greater than the annual average of South America ( 1.600 mm); and the hydric availability (39,032 L·s-1·km2) of the studied system is less than the hydric availability mean for Colombia (58 L·s-1·km2) and greater than the hydric availability mean for South America (21 L·s-1·km2).