research was conducted for evaluating an alternative management under evaporation stress of the reservoir El Cuchillo, which supplies water to the Metropolitan Area of Monterrey (AMM, Spanish acronym) located in the state of Nuevo León, Mexico. The surface sources of water supplies for the AMM come from three reservoirs: La Boca, El Cuchillo and Cerro Prieto, which are integrated in a single system and exchange water with two reservoirs, Marte R. Gómez and Las Blancas. Due to high temperatures during the whole year, especially in the summer, as well as the big surface area of the pool, El Cuchillo is a big source of water loss by evaporation. This research conducted an analysis to achieve alternative scenarios for water management in reservoirs facing this problem, by applying the model HEC-ResSim. This model, created by the US Army Corps of Engineers, has a multi reservoir simulator and can simulate water resource systems from many sources. The present study used monthly observed data from 1994 to 2014 of reservoir volume, inflow and diversion; in addition, hydraulic data from the reservoirs were used to develop the numerical model. The results show that it is possible to increase the reservoir diversion and obtain 50 % more water for the scenario 1 and 70 % more for the scenario 2 during a period of 20 years from 1994 to 2014, if these cycles of evaporation are taking in consideration.