Water transpired by weeds could exacerbate crop drought stress in dry periods through increasing soil moisture deficits, resulting in a decrease in crop water use efficiency. However, weed-crop competition for water is dynamic as water uptake depends on the relative growth of the crop vs. the weeds and plant stress status depends on the amount of solar-radiation intercepted and the degree of depletion of soil water reserves. To evaluate dynamic outcomes of crop-weed competition, a simulation model was developed and additive experiments established to test the model, with corn in monoculture and in combination with high-density stands of velvetleaf - A. theophrasti M.. The model considers individual plants to estimate canopy light interception and scales the root zone of influence to plant biomass to estimate profile water uptake. Despite exceptionally dry conditions in some years, we found no evidence that the corn-weed mixtures had less total soil water or different rates of water extraction trough the profile than the corn monocrop. Furthermore, time series monitoring of stomatal conductance and end of the season harvest index suggest that corn was no more water stressed in the weedy treatments. Together, these data imply that soil water dynamics and drought severity were not significantly affected by weed competition. The similarity of canopy light interception for maize systems with and without weeds may explain the somewhat counter-intuitive nature of our findings. The model will be used to test the impact of weed competition on corn WUE under a range of contrasting weather scenarios.