A quarter-century ago, San Diego and its suburbs imported 95% of their water supplies. Thanks to investments in desalination and other efforts to boost supplies, that figure has already dropped to 57% and is projected to fall to just 18% sometime in the next two decades.

San Diego has gone from being one of the most vulnerable areas of California during drought to one of the best prepared—and in so doing has become a model for the future of water use in cities.