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The understanding of water balance components at a watershed level is critical to the analysis of possible improvements to water resources management. The assessment of some of these components is difficult because of the lack of available data. Thus, the use of hydrological models is a valuable tool. For a group of watersheds located in the southern Maule Region in Chile, which constitute a complex irrigation district, the Water Balance Simulation Model (WaSiM-ETH Version 2, Distribution 7.5, Schulla, 2006) was used to simulate the agricultural water distribution and use, taking into consideration crops, soil management and irrigation practices. In the study area, irrigation water originates from a range of sources, including watersheds outside of the district. The distribution of water was defined using the distribution of irrigation canals and the farmers' water rights. Soil-use maps were elaborated using the Chilean Agricultural Survey of 1997, and evapotranspiration was estimated using crop coefficients. The model was calibrated for the period 1995 and 1998 and validated for the period 1999 to 2001, using a spatial resolution with cell size 2000 m.