PHOENIX (AP) — Gripped by a prolonged drought, Arizona faces possible cuts to its main water supply in the next 18 months.
Residents, however, face none of the restrictions that neighboring California has imposed this year.
The desert state has been able to withstand a 15-year arid spell through long-term planning, conservation and a massive underground reserve that holds enough water to supply the state for a year.
But dropping water levels at Lake Mead, the largest water reservoir in the U.S., could prompt cuts that state-level officials are looking to avoid. The lake, formed by the Hoover Dam, has been dipping for years and federal officials say it could drop low enough by 2017 that it would trigger supply cuts to Arizona and Nevada.
Arizona would lose more than 11 percent of the water it gets through the Central Arizona Project canal system, or about 320,000 acre feet, until lake levels recover. Nevada would lose 13,000 acre feet, Mexico 50,000, and California — the senior water rights holder — none.
The Arizona cuts would be roughly enough to supply 600,000 homes, but the cuts would only affect farmers.
Those farmers will likely be able to pull from their own wells to supplement their irrigation supplies, according to Tom Buschatzke, director of the Arizona Department of Water Resources.
Water managers in Arizona, Nevada and California, however, are wary of even deeper cutbacks prompted by lower lake levels.
To prevent that, they've taken steps to limit the amount of water they're pulling from the Colorado River, which feeds the lake.
Under an agreement reached late last year, Arizona will forego 345,000 acre feet of water over three years, more than the total amount it expects to lose in 2017 if federal officials declare a shortfall. Nevada would lose 45,000 acre feet, and California committed to saving 300,000 acre feet through conservation efforts. The goal is to raise Lake Mead's level by as much as 10 feet.
Arizona uses about 7 million acre feet of water a year, 70 percent of that for agricultural use, 22 percent for municipal use and the rest for industrial consumption. The state has nearly 9 million acre feet of water stored underground.
The Colorado River provides 40 percent of the state's water through a 336-mile system of aquaducts that bring water to the Phoenix and Tucson metropolitan areas. Another 40 percent is pumped from underground and most of the rest comes from mountains that feed Arizona's river systems.
Deeper drops at Lake Mead, which could come if the drought in the Rocky Mountains persists, could lead to even deeper use reductions in about a decade.
There would be years of warning, but municipal, industrial and tribal users would face cutbacks. Such a drop-off would also require new wells to tap into the water stored underground.
Arizona's water buffer can be credited to a landmark 1980 law that requires storage, the identification of water supplies for new development in urban areas, conservation measures and a cap on agriculture acreage.
"So, basically, as agriculture was replaced with some other use, houses and industry, you couldn't go next door and blade up a piece of the desert and put in new agriculture," Buschatzke said.
The conservation measures led to most new homes having low-water use yards and fixtures. The state's renowned golf courses are limited in how much water-thirsty grass they can plant.
In fact, despite growing from 1.1 million residents in 1957 to more than 6.5 million today, the state uses essentially the same amount of water.
David Modeer, president of the Colorado River Water Users Association, said Arizona is in good shape for now.
But Modeer, who remains a consultant on the Central Arizona Project after retiring as director last month, warns that big cuts would loom if average snowfalls don't return to the Rockies, since that range feeds the Colorado River.
"Without a break in the drought that's a strong possibility of reaching that level," Modeer said.
In a worst-case scenario, even California's supplies would be in jeopardy, he said. If Lake Mead storage levels get low enough, Modeer said, "then I guess in common words it'd be all bets are off."