Bathtub rings around Lake Mead

There's a huge crisis brewing in the western US - about water. Lake Mead, a reservoir east of Las Vegas that when full, holds 9.3 trillion gallons, is drying up. This water is used to irrigate a million acres of farm land in the US and Mexico, supplies water to millions of people, powers the Hoover Dam which in turn powers a half-million homes and powers the pumping of water across the Sierra Nevada Mountains into Southern California.

This article sheds some light on how fast this water is disappearing.