Continental and global-scale groundwater models have been proposed recently to complete and improve the simulation of the hydrologic cycle. This development is still impeded by the resolution of these models either due to data availability and/or computational demands. One of the major challenges is determining the location of surface water bodies on the global scale based on land surface elevation data, as surface water elevation directly influences the model results. Closely connected to this problem is the comparison of simulated model results to observations of depth to groundwater. The models calculate hydraulic head so depth to groundwater is heavily influenced by how the variation in topography is reflected in one computational cell. This presentation demonstrates by means of the newly developed global groundwater model G³M that depth to groundwater observations need to be contemplated in the context of the elevation of the surface water bodies to draw proper conclusions on the model performance. The impact of uncertainty in surface water body elevation is illustrated based on multiple grid size experiments (5 arcmin, 30 arcsec, and 3 arcsec resolution) for New Zealand.