Water and the Central Arizona Project

Arizona is the fifth-driest state in the country. Its two largest cities together hold more than five million people in a desert that receives roughly eight inches of rain per year. The question of how Arizona got to be this populated is inseparable from one engineering project: the Central Arizona Project.

The CAP, as everyone calls it, is a three-hundred-thirty-six-mile aqueduct system that carries Colorado River water from Lake Havasu, on the Arizona-California border, uphill to Phoenix and Tucson. It is the largest single water delivery project in the United States. Construction began in nineteen seventy-three and the first water reached Phoenix in nineteen eighty-five. The total cost was more than four billion dollars.

Getting the water required decades of legal and political combat. Arizona had been fighting California over Colorado River allocations since the nineteen twenties. The Colorado River Compact of nineteen twenty-two divided the river among seven states, but California consistently drew more than its share and Arizona lacked the infrastructure to use its own allocation. The Supreme Court settled the core dispute in nineteen sixty-three, in Arizona versus California, ruling that Arizona was entitled to two point eight million acre-feet of Colorado River water per year.

Building the project required acts of Congress, multiple federal agencies, and a generation of Arizona politicians, most prominently Senator Carl Hayden, who served Arizona in Congress from nineteen twelve, the day it became a state, until nineteen sixty-nine.

Today the Colorado River itself is over-allocated. Drought and decades of overuse have dropped Lake Mead and Lake Powell to historic lows. The water deals that built modern Arizona were signed when the river was carrying more water than it ever carried again.