Reuters: Chances are about even that Lake Mead, the prime source of water for the desert city of Las Vegas, will run dry in 13 years if usage is not cut back, according to study released on Tuesday. The finding is the latest warning about water woes threatening the future of the fast-growing US casino capital and comes amid a sustained drought in the American West. The study by two researchers at the Scripps Institution of Oceanography at the University of California San Diego, …