Climate change is predicted to create increasingly arid deserts with fewer and smaller water sources. Because free water is already limiting for arid-adapted animals, reductions in water likely will impact desert species and how they compete for this limited resource. Our objective was to examine how the size of water sources influenced competition between 2 ecologically similar bats, Parastrellus hesperus and Myotis californicus, in the American Southwest. Bats are a highly successful taxon in deserts, although many rely upon access to free water. We examined bat activity observationally over 35 different-sized water sources throughout the Mojave Desert in southwestern Utah, United States, and experimentally reduced the surface area of 2 water sources. Parastrellus hesperus and M. californicus typically occurred at the same water sources, but both species temporally partitioned their use of shared water sources regardless of the surface area of the water. Experimentally reducing surface area of water sources negatively affected drinking behaviors of both species and resulted in higher overall activity, but temporal partitioning still occurred. While loss of water may influence some competitive interactions, mechanisms such as temporal partitioning can potentially allow continued co-use of limited resources by competing species.