"Southern California gets the vast majority of its water from four aqueducts that flow from the north, but all of them cross the San Andreas Fault."

That means millions of people are just one major earthquake away from drying out for a year or more.

"'It's a really concerning issue for the city of Los Angeles,' says Craig Davis, an engineer with the LA Department of Water and Power, which oversees the LA aqueduct."

"Research shows that a magnitude 7.8 quake on the San Andreas Fault could sever all four aqueducts at once, cutting off more than 70 percent of the water sustaining Southern California."