When the Carlsbad desalination plant opened in December 2015, regional water officials gushed about how reliable it would be. San Diego could now drink from the endless Pacific Ocean rather than be stuck depending on rain and snowmelt to come from hundreds of miles away. So far, though, the plant has not been as reliable as promised. Over the last year, the privately owned plant failed to deliver nearly a fifth of the water the San Diego County Water Authority ordered from it.