The goal of this study was to determine the actual water budget for Taubaté, SP and investigate the future water availability. The Thornthwaite-Mather (1955) method was used for the climatological water budget combined with observed and simulated data of air temperature and precipitation. The future scenarios indicate an increase of temperature (ranging from + 0.5 °C to + 2.7 °C) and precipitation (ranging from 80 to 150mm). These results will provoke an increase of the water deficit (ranging from 50 to 80mm) and a decrease of the surplus of water (around 200mm). The increase of the precipitation will not be sufficient to compensate for the increase of the water demands from evapotranspiration