The most important thing to understand: If you’re reading this, you live in a desert. And you can live in this desert because politicians, scientists and engineers have moved mountains, almost literally, to bring you life-giving water. The latest brawl in Water World plays out on this backdrop, and what comes out of your tap may well depend on the result. Will it come from recycled waste water? Desalination plants? A giant tunnel or two under the Delta? The answers will, in large part, depend on who’s chosen to lead the gargantuan Metropolitan Water District of Southern California, which provides water to 19 million people from Ventura County to the Mexican border.