Arizona’s Water: Uses and Sources
A land’s carrying capacity has always been determined by its access to usable water. Humans use water primarily for irrigation, industry, drinking water, and sanitation. Millions of non-human species depend on water for life itself. Only 1% of the earth’s water is freshwater, to be shared among more than 7 billion people and all freshwater aquatic ecosystems in the world. It is perhaps the most precious resource on the planet.
Large volumes of water are most commonly measured in acre-feet. One acre-foot is the amount of water required to cover one acre of area to the depth of one foot: 325,851 gallons. Approximately one acre-foot serves the needs of a family of five for one year. Arizona is one of the driest states in the U.S., and one of the fastest-growing. Arizona's current population is over 6 million (2010 Census) and is projected to grow to as many as 9.5 million people by 2025. Encompassing four deserts, Arizona receives a statewide average of only 12.5 inches of rain per year. Our climate presents intense challenges in balancing our water needs between ourselves, our neighbors, and our riparian ecosystems. Water has defined our past and will determine our future.
All economic activity, including mining, agriculture, and urban growth, relies on a dependable water supply. But our historic overuse of water has destroyed ecosystems and is causing dangerous changes to the land. To meet these challenges, Arizona has developed one of the most advanced water management systems in the world. Networks of dams, canals, and replenishment ponds store water and move it when and where it is needed. Years of negotiations with our border states, Mexico, and users within the state have yielded a complex system of water allocation laws. Conservation initiatives strive to protect wetlands and restore endangered species. But to understand Arizona’s water story, first we must consider where we get water and how we use it.
Water Budget: Usage and recharge
How much water do we use?
Based on Arizona Department of Water Resources (ADWR) data from 2001–2005, Arizona uses approximately 6.96 million acre-feet of water annually. A 2008 estimate by the University of Arizona Water Resources Research Center places that value as high as 8 million acre-feet. Collaborative estimates place the actual water used in Arizona at between 7.25 million and 7.75 million acre-feet annually. That’s about 2.4–2.5 trillion gallons a year.
How do we use water?
Water in Arizona is used for cultural purposes (for and by people) and for in-stream uses, such as for the support of fish and riparian ecosystems.
Arizona's cultural use of water. Values based on Arizona Department of Water Resources.
The largest cultural use is agriculture—using approximately 69% of the available water supply in Arizona. In the past, this percentage was as high as 90%. Reductions have been the result of urbanization of agricultural lands, and the result of heavy investment in conservation measures—by the irrigated agriculture industry—done both on the land and in the delivery systems.
Industry uses about 6% of Arizona’s water supply, or 400,000 acre-feet. Arizona’s major industrial uses come from mining and power generation. Arizona supplies over 60% of the nation’s copper and mines substantial industrial minerals. Power, a growing industry in the southwest, uses water too. One kilowatt hour of electricity takes about 25 gallons to produce. Fortunately, power generation can use effluent, or recycled water. Palo Verde Nuclear Generating Station is the only nuclear plant in the world to use recycled water in its cooling ponds. About 70% of the water used to produce power in Arizona is effluent. Many golf courses in Arizona also take advantage of recycled water and use it for irrigation.
Municipal use is estimated at about 25% or 1.6 million acre-feet, and much of this is used to irrigate landscapes. While efforts are being made to transition from traditional landscaping to xeriscape (replacing high-water use plants with native specimens), a growing population still means an increased use of municipal water.