The Metropolitan Water District, which provides water to six counties in Southern California, announced a partnership on Wednesday, Oct. 13 with Arizona water agencies to collaborate on planning for what could become one of the nation’s largest water recycling plants, producing up to 150 million gallons daily to serve more than 500,000 homes.

Central Arizona Project will provide $5 million and the Arizona Department of Water Resources will provide $1 million for environmental planning of the Regional Recycled Water Program, which will purify treated wastewater to produce a new, drought-proof water supply for Southern California. If the full project is developed, it would cost $3.4 billion and improve sustainability of Colorado River water supplies.