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Metropolitan Phoenix is situated at the northern edge of the Sonoran Desert in the Basin and Range Physiographic Province of the western U.S.  Although the city receives an annual average of only 8.29 inches of rainfall, its dryland rivers, the Salt and Verde, drain more humid mountain watersheds.  Three upland watersheds provide the city with approximately 1 million acre-feet of water per year.  This regional supply is augmented by Colorado River water through the Central Arizona Project, a 336-mile aqueduct that delivers water from the Colorado River at Lake Havasu City to Central Arizona, in addition to groundwater from large alluvial aquifers.  Underground water has been used as a hedge against drought when surface water is in short supply.  Together these sources provide approximately 2.3 million acre feet per year to the Greater Phoenix region. Of this, approximately 40% is used for agricultural purposes, and the remainder is used to support municipal and industrial uses (Larson et al., 2006).  Municipal water consumption will rise as agricultural lands are retired and turned over to urban uses in the face of rapid population growth.  Approximately 50% of the municipal use occurs in the single-family sector (Wentz and Gober, 2007). 

Historically, water in the Phoenix area has been tightly managed by a set of agreements, regulations, and institutions that have evolved to allocate water in a desert environment.  Water management decisions are made on a local water provider level, with the City of Phoenix being the largest regional provider.  Some 40 large providers and 80 small providers manage and distribute supplies from the Salt and Verde watersheds, Colorado River water, and underground water, in addition to implementing water education programs and setting prices (Figure 3). Water in Phoenix is not, in the main, allocated to users based on market mechanisms, but instead by a set of legal and political agreements that ensure an inexpensive supply to municipal and agricultural customers.  Residential customers in the City of Phoenix customers pay only $1.65 for one ccf (748 gallons) during the low-use months of December, January, February, and March; $1.97 in April, May, October, and November; and $2.65 in the high-use months of June, July, August, and September.

Map of Phoenix area water providers
Click on the picture above for a map of Phoenix area water providers