Water, Water, . . . Everywhere, . . .

. . . but less and less.

Lake Mead is presently at the lowest levels sine it was first filled-up after construction of the Hoover Dam. 

And, . . .  and "the watershed is now so parched and depleted that Mead is projected to continue dropping next year and into 2023.

The watershed has been ravaged by one of the driest 22-year periods in centuries. Scientists describe the past two decades as a megadrought worsened by climate change, and say the Colorado River Basin is undergoing “aridification” that will complicate water management for generations to come.

In 2000, Lake Mead was nearly full and its surface was lapping at the spillway gates of the Hoover Dam. Since then, the reservoir has fallen nearly 143 feet. And it's now at the lowest levels since 1937. "

Ref: USA Today 

Ref: U.S. West prepares for a first-ever water shortage declaration

What happens to the glamor of Las Vegas when the toilet in your hotel room doesn't flush anymore?

To answer DonDiego's question: metered hotel room toilets. $5 a flush. The good news is, you'll be able to use players' club points.

The story of the Colorado River watershed and how it has been, uh, managed is fascinating. The Colorado River Compact of the 1920s actually allocates more water (in millions of acre-feet) to Nevada than it has ever used. Now, if the state wants that water, it'll have to legally or otherwise wrench it away from Arizona and California. Hilarity will ensue. I recommend Marc Reisner's "Cadillac Desert" and "Where the Water Goes: Life and Death Along the Colorado River" by David Owen, both fascinating reads, to explain why Vegas is now up a dry creek without a paddle.

Aside from over-allocation of the river's water (referred to charmingly as a "deficit"), there's the problem of that nonexistent fake news liberal hoax Chinese conspiracy climate change, which has resulted in much lower precipitation in the upper and lower Colorado basins than was ever planned for. Vegas is going to have to start acting like a desert city.

Water desalinization will be the next big challenge to conquer for scientists seeking the Nobel prize.   
Right now it's too costly although I think San Diego has a project in the works.     

short of that I think the Southwest and Vegas are in trouble.    Doesn't help that the population is exploding there.   If the river dries up maybe they'll move everything to Tunica. :)