The water problem is a lot bigger than that. North American cities have mostly polluted the rivers they lie on and can't use them for a water supply. E.g. Atlanta gets its water from Lake Lanier, not the Chattahoochee. New York gets its water from the Catskills, not the Hudson.
Many cities are facing water shortages. Not just Las Vegas and Phoenix. The Colorado is tapped out, and California, Arizona, and Nevada have been fighting over it for decades. Rainy humid Atlanta was facing water usage controls for several years around 2007-2009. The Floridan aquifer is tapped out--developers are having to dig wells 1,000 feet deep these days to get water. Fracking is in danger of contaminating the Ogallala along with all the water that makes agriculture possible in the breadbasket. San Francisco is not yet in dire straights but Hetchy-Hetch isn't immune to the water problem.
These are all still localized problems, with local solutions (or that are in need of local solutions). Speaking about water shortages on larger scales seems to ignore the reality of how water supplies work.
Many cities are facing water shortages. Not just Las Vegas and Phoenix. The Colorado is tapped out, and California, Arizona, and Nevada have been fighting over it for decades. Rainy humid Atlanta was facing water usage controls for several years around 2007-2009. The Floridan aquifer is tapped out--developers are having to dig wells 1,000 feet deep these days to get water. Fracking is in danger of contaminating the Ogallala along with all the water that makes agriculture possible in the breadbasket. San Francisco is not yet in dire straights but Hetchy-Hetch isn't immune to the water problem.