San Diego water officials were dealt a major legal loss Wednesday that could leave local water customers on the hook for billions of dollars over the next several decades. For years, San Diego water officials have argued that the region’s major supplier of water, the Metropolitan Water District of Southern California, has been charging too much to deliver water to San Diego from the Colorado River. But on Wednesday, an appellate court found that San Diego water customers are, by and large, only being asked to pay their fair share to use a statewide water delivery system.