“In short, it will become very expensive to pump that deeper groundwater on our current trajectory, so that only the wealthiest farmers and the biggest farms will be able to afford to pump that groundwater,” he said.

The effects are already being seen in communities like Wenden in La Paz County. Wells are running dry, and residents are already paying up to $130,000 for new ones.

“People used to say the Colorado River was the lifeblood of the Southwest US,” Arizona State professor Jay Famiglietti, the study’s senior author, told me. “Now it’s the groundwater. We need to make sure we take precautions to sustain that groundwater for multiple generations in the future.”

“We have to be worried,” Karem Abdelmohsen, the lead author of the study and a research scholar at Arizona State University, said. “This is really scary.”

That’s because the Colorado River basin is already struggling with water scarcity. Covering seven states, as well as parts of Mexico, it supplies water to about 40 million people and supports billions of dollars in agriculture.

“We’re using it faster and faster,” said Jay Famiglietti, an Arizona State University professor and the study’s senior author.

In the past two decades, groundwater basins – or large, underground aquifers – lost more than twice the amount of water that was taken out of major surface reservoirs, Famiglietti’s team found, like Mead and Lake Powell, which themselves have seen water levels crash.

New research from Arizona State University professors shows the Lower Colorado River Basin has lost as much groundwater as is contained in Lake Mead over the past 20 years.

"We're losing a lot of water," said Jay Famiglietti, an Arizona State University professor in the School of Sustainability.

In the last 10 years, the water depletion was three times faster than the decade before. The vast majority of the loss was groundwater.

Arizona State University professor Jay Famiglietti co-authored the paper and says the loss comes from climate change, population growth.

“It's in part a lack of management. And if we want to survive and, you know, eat food, because, again, most of our water is used to produce food if we want to be doing that for decades and decades and centuries, now is the time to make those changes," Famiglietti said.

“The work suggests that, in states like Arizona, where only 18% of the area of the state has groundwater management, that expansion of groundwater management across the entire state is a critical step towards preserving this precious resource for future generations and for long-term economic vitality in the region,” Jay Famiglietti said.

Meanwhile, underground water supplies continue to shrink to the point that some wells in rural areas have gone dry. Residents are faced with the choice of drilling deeper, hauling water or moving, said Sarah Porter, director of the Arizona State University Kyl Center for Water Policy. Managing the groundwater won’t reverse the decline but can slow it, she said.

Famiglietti noted that it is almost impossible to know how much groundwater is ultimately available for humans — and the cost required to access it by drilling ever deeper wells also varies dramatically by area. “What we do know is that water tables are falling, that the ground is subsiding,” he said. “We know bad things are happening.”

“The more surface water we lose from the Colorado River, the more pressure there’s going to be on the groundwater,” Famiglietti said. “And then it becomes a ticking time bomb.”