Wholesale water rates adopted Thursday by the San Diego County Water Authority Board of Directors include some of the smallest increases in the past 15 years due to successful litigation against the Los Angeles-based Metropolitan Water District of Southern California and strategic use of financial reserves, the agency said. They also highlight a historic shift in water costs: The Water Authority’s independent supplies from the 2003 Colorado River Quantification Settlement Agreement are now less expensive for the region than supplies from MWD, and that difference will grow in the years ahead.