As a worsening drought forces millions of Californians to face mandatory water restrictions, one corner of Southern California has largely shielded itself from supply-related woes: San Diego County.

For Western water planners, the path it took to get there serves either as a blueprint or a cautionary tale.

Over the past three decades, San Diego County diversified its water supply, ramped up conservation and invested in big-ticket water infrastructure including the Western hemisphere’s largest desalination plant, which removes salt and impurities from ocean water. As a result, the water agency that serves 24 water utilities including the city of San Diego says it can avoid cuts until at least 2045, even during dry periods.