In the semi-arid crystalline area of Ceará, the exploitation of alluvial aquifers for irrigation and domestic supply to rural communities over the last 10 years has upset the traditional mechanisms of water resources management. In the Forquilha watershed (Quixeramobim-CE), the main water resources are reservoirs (1 to 7 hm3), and an alluvial aquifer (2.3 hm3). From 1998 to 2006, pumping of alluvial groundwater for irrigation supply increased from ~0 to 0,7 hm³/year, and the fraction of population supplied through domestic water networks, using reservoirs and the aquifer, increased from 1% to 70%. Physical and socioeconomic issues were used 1) to characterize the system, 2) to build future scenarios of water resources exploitation, and 3) to build hydrological balance models in order to simulate the different impacts on water resource availability and salinity. Simulation results showed that, releases from the upstream main reservoir are necessary to keep reservoir salinity below 0.7 g/L and for guaranteeing domestic needs in the whole watershed. Moreover, the simulations showed that the area of irrigated fields cannot increase beyond the current extent (75 ha) without serious problems with water availability and salinity in the whole watershed. Otherwise, important socioeconomic problems are expected.