Thanks in part to all of the stunning imagery coming out of the drought-plagued West, it's easy to see the rapid decline of the region's water supply in motion. But according to a new study from scientists at NASA and the University of California, Irvine, the loss of water you can't see is actually happening at a much more rapid and dire pace than that of the water you can see, leading scientists to declare that the West's water supply may be under threat.

The study found that over the last 10 years, 75 percent of all water loss — some 41 million acre feet of freshwater — in the Colorado River Basin came from vital underground groundwater resources. And that's important, because as NASA notes, the Colorado River provides 40 million people in seven states in the southwestern United States with drinking water.

"We don't know exactly how much groundwater we have left, so we don't know when we're going to run out," Stephanie Castle, a water resources specialist at the University of California, Irvine, and the study's lead author, said in a press release. "This is a lot of water to lose. We thought that the picture could be pretty bad, but this was shocking."

Data for the study was collected from NASA's GRACE satellite, which measures the variation in strength of a given area's gravitational pull over time based on changes in the mass of a region due to alterations in water levels.

Simply put: When there's more water, the mass rises in the area causing the gravitational pull in the area to rise as well. On the flip-side, when there's less water, the mass drops in the area and the gravitational pull declines in the area.

The data revealed that states were pumping more water from underground resources in the Colorado River Basin to compensate for the loss of surface water during a more than decade-long drought. That's particularly problematic given the regulation differences of water above and below ground.

Surface water in the Colorado River Basin is regulated and monitored by one centralized authority, the U.S. Bureau of Reclamation, allowing for a more stringent preservation of resources. But the water underground is pumped by several states and is largely unmonitored, NASA notes.

The consequences of that lack of monitoring will inevitably be felt at the surface level and in the households of the 40 million-plus who rely on the Colorado River, according to Jay Famiglietti, a senior author on the study.

"Combined with declining snowpack and population growth, this will likely threaten the long-term ability of the basin to meet its water allocation commitments to the seven basin states and to Mexico," Famiglietti said.

And that could mean that it may be a matter of when, not if, the West officially runs dry.

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A buoy warning 'no boats' stands on dirt at the abandoned Echo Bay Marina on July 13 in the Lake Mead National Recreation Area, Nevada. The marina closed last year after no businesses wanted to operate it, in part due to falling water levels according to the National Park Service. (Photo by Ethan Miller/Getty Images)