In the arid West, nothing happens without access to water—no cities, no agriculture, no industry, no tourism, no people, nothing.

Water is quite literally life.

And that's a dire thought for about 20 million Americans, as the largest source of fresh water for most of the desert southwest is going dry—and it's happening fast.

Lake Mead, the largest man-made reservoir by volume in the U.S. and which supplies drinking water and electricity for cities like Los Angeles, Las Vegas and Phoenix, is now at just 39 percent capacity and forecasters say its only going to get worse, with water cuts becoming more and more likely by 2016.

The Las Vegas area—with over 2 million residents and over 40 million visitors every year—is in particular peril, as it's dependent on the lake for 90 percent of its drinking water.

Officials say that there is enough water for the rest of this year and next year. But after that the chances of water rationing rises to about 50-50.

"We will meet our water orders this year and we are not projecting a shortage condition in 2015," said Lower Colorado Regional Director Terry Fulp in a statement released on Tuesday. "We continue to closely monitor the projections of declining lake levels and are working with stakeholders throughout the Lower Basin to keep as much water in Lake Mead as we can through various storage and conservation efforts."

According to the Bureau of Reclamation, the projected lake elevation of around 1,080 feet above sea level expected in November will be the lowest recorded level since Hoover Dam was completed in 1936. The previous low-level mark was 1,082 feet recorded in 2010.

The normal surface elevation of the lake, which was last full in 1998, is about 1,296 feet above sea level. State and federal officials have worked out plans for a shortage declaration, which would cut water delivery to Arizona and Nevada if the elevation of the lake drops below 1,075 feet—which Bureau of Reclamation officials say could happen as soon as 2016.

The Southern Nevada Water Authority is constructing a new, three-mile long tunnel to pump water from the lake at elevations as low as 1,000 feet above sea level. It's expected to be completed sometime in 2015.

"As lake levels continue to drop as we've seen over the past 14 years, the threat of the lake dropping below one of the existing intakes could have impacted about half our capacity," Bronson Mack of the Las Vegas Valley Water District told ThinkProgress.

Image via Weather Channel

The dropping water levels, brought on by historic droughts in 2012 and 2013, have left a roughly 130-foot high "bathtub ring" of white minerals deposited on the rock ledges around the lake.

Lake Mead is largely fed by springtime melt from the snowpack in the high country of Colorado and Utah into the Colorado River—an amount of water that can vary greatly from year-to-year.

Compounding the problem, the population of the Southwest continues to boom while climate change is making the the entire region even hotter and drier.

Upstream from Lake Mead on the east side of the Grand Canyon, Lake Powell—which provides water and electricity across much of the upper Colorado River basin—is doing a little bit better at roughly 52 percent capacity but is also facing grim drought-related future.

Top image via National Geographic