Surrounded by miles of creosote and ocotillo in the Sonoran Desert, state officials and business leaders gathered in October against the backdrop of the ragged peaks of the White Tank Mountains to applaud a plan to turn 37,000 acres of arid land west of Phoenix into the largest planned community ever proposed in Arizona. The development, Teravalis, is expected to have 100,000 homes and 55 million square feet of commercial space. But to make it happen, the project’s developer, the Howard Hughes Corporation, will need to gain access to enough water for its projected 300,000 residents and 450,000 workers.