After more than two decades of drought, water utilities serving the largest urban regions in the arid Southwest are embracing a drought-proof source of drinking water long considered a supply of last resort: purified sewage.

Water supplies have tightened to the point that Phoenix and the water supplier for 19 million Southern California residents are racing to adopt an expensive technology called “direct potable reuse” or “advanced purification” to reduce their reliance on imported water from the dwindling Colorado River.

“[Utilities] see that the river is overallocated, and they see that the climate is changing,” said Kathryn Sorensen, former director of Phoenix Water Services Department. “They’re looking at this and understanding that the river supply is highly variable and extremely uncertain in the future.”

The Colorado River that sustains nearly 40 million people and more than 4 million acres of cropland across seven states is shrinking because of climate change and overuse. The river’s flows have declined approximately 20 percent over the past century, and a more than two-decade drought that began at the turn of this century has pushed the system to its limits.

With so much at stake, cities dependent on the river are strengthening water conservation measures and pursuing new sources of water with urgency.

READ MORE at the Water Education Foundation.