The resource dispersion hypothesis (RDH) proposes that in a spatially and temporally heterogeneous environment the territory size of social carnivores increases as the dispersion of limited resources is more widely spaced, whereas group size is limited, independently, by the richness or abundance of those resources or key habitats. To assess if white-nosed coatis Nasua narica behave in accordance with the RDH, the relationship between home-range size and spatio-temporal availability of resources in Mexican tropical dry forests with marked seasonal rainfall was examined. Specifically, home-range sizes were compared at two study sites that were broadly similar but contrasting in resource abundance and dispersion. Home-range estimates for seven white-nosed coati bands varied between 45 and 362 ha. Home-range size did not correlate with food resource abundance and was better explained by the dispersion of water sources during the dry season. Average home-range size was three times greater at the site where water sources were more widely separated during the dry season. These results are in accordance with the predictions of the RDH, and provide an example where the critical resource determining range size and configuration is water.