This paper establishes the complexity of determining the "public" or "private" nature of water delivery systems, by analyzing the genesis and evolution of one water system in the Western U.S.: the Salt River Project. The kind of cooperative model that has most often been documented in small coops in developing countries can also be seen in the U.S. with its vast socio-technical network that has been developed since 1900. Originally mainly an effort to help rural farmers, the Salt River Project has undergone a shift towards an emphasis on economic and urban growth and servicing major cities in central Arizona. How this shift was possible and its current implications are problematized in light of sustainability of the SRP model despite increasing water scarcity in the West