Groundwater flow simulation in the Tecocomulco sub-basin confirms its local discharge nature. This upward flow supplies boreholes, dug-wells and the Tecocomulco lagoon. From a regional perspective, this sub-basin recharges the neighbouring Apan and Singuilucan sub-basins, and the Mexico basin. Despite the fact that the Tecocomulco plain is a local discharge zone, unplanned groundwater withdrawal and land-use changes have led to the drying of the lagoon. Landuse change causes an increase in surface runoff inducing an estimated 35% decrease in recharge. Modelling reproduced initial conditions and observed drawdown levels from where the hydraulic and hydrological functioning of the Tecocomulco lagoon was proposed. Modelling assisted in verifying effects caused by current groundwater withdrawal. Time dependant desiccation of the lagoon was reproduced independently of borehole location. Maximum allowable simulated additional increase in groundwater withdrawal was 0.1 m3 s-1. Strict surveillance of land-use and reforestation practices in the sub-basin is needed to avoid the disappearance of the lagoon.