We evaluated how different configurations of a large-scale river basin model affect simulations of streamflow, evaporation, soil moisture, and groundwater in the Po River Basin in Italy. We tested alternative soil depths and the inclusion or removal of subsurface flow pathways, and compared results with observations and with an established long-term water balance relationship. Setups that best matched river flow often underestimated evaporation and overestimated deep groundwater recharge.