Leak Mead – on your left, when you drive from Las Vegas across the Hoover Dam – is the largest reservoir in the country when at capacity. It’s fed by the Colorado River which provides water for agriculture, industry, and 40 million people in Nevada, Arizona, California, and Mexico, including Los Angeles, San Diego, Phoenix, and Las Vegas. Now after 15 years of drought, the “lake” – a mud puddle surrounded by a huge chalky bathtub ring – is threatening to run dry.

It’s considered “operationally full” when the water level is at 1,229 feet elevation above sea level. On May 2, the water level was down to 1,078.9 feet above sea level, the lowest since it was being filled in May 1937. It’s down 15 feet from the same day a year ago. Over the last 36 months, the water level has dropped 44.8 feet. It’s down 150 feet from capacity.

If the water level is below 1,075 feet elevation – 4 feet below today’s level – by January 1, 2016, it will trigger a federal water emergency. And water rationing. Las Vegas Review Journal reported that forecasters expect the level to drop to 1073 feet by June, before Lake Powell would begin to release more water. Assuming “average or better snow accumulations in the mountains that feed the Colorado River – something that’s happened only three times in the past 15 years,” the water level on January 1 is expected to be barely above the federal shortage level.

Even with these somewhat rosy assumptions of “average or better than average snow accumulations,” the water level would begin set new lows next April. But if the next winter is anything like the last few, all bets are off.

If the level drops below 1050 feet, one of the two intake pipes for the Las Vegas Valley, which gets 90% of its water that way, will run dry. A new $817-million tunnel is being built by the Southern Nevada Water Authority to create a new drain to get the last drop out of the bathtub. It should be ready by September.

The LA Times explains what water rationing would mean for the states:

Las Vegas has long been at a disadvantage when it comes to Lake Mead water. A 1922 Colorado River water-sharing agreement among seven Western states — one still in effect nearly a century later — gives southern Nevada the smallest amount of all; 300,000 acre-feet a year, compared with California’s 4.4 million annual acre-feet. An acre-foot can supply two average homes for one year.

This summer, officials will make their projection for Lake Mead water in January 2016. If the estimate is below 1,075 feet, rationing kicks in: Southern Nevada would lose 13,000 acre-feet per year and Arizona would lose 320,000 acre-feet. California’s portion would not be affected.

Note the last sentence – that California would not be affected. Keeping lawns green in LA is top priority.