Tucson is located in the semi-arid northern reaches of the Sonoran Desert in southeastern Arizona, with mountains on each side - the Santa Catalinas to the north, the Rincons to the east, the Tucson Mountains to the west, and the Santa Ritas to the south. Most of the population of the greater Tucson area lives between these mountain ranges in the Santa Cruz River Valley. In addition to climatic factors, population growth, and increasing municipal and industrial demand are the most important drivers of water supply in Arizona today (AWI 2008:16) and this is true for Tucson as well.