In 1992, prospectors in Los Angeles hatched an idea for a new water supply that was improbable and speculative, even by Southern California standards. Far off in the Mojave Desert, beneath the flat dry lake bed of the Cadiz Valley, millennia’s worth of groundwater could be pumped and piped 43 miles to the Colorado River Aqueduct, the crown jewel of the Metropolitan Water District’s massive web of infrastructure. The water then could be sold to any of the 26 member agencies of the MWD.