Two years after losing in court and six years after being rejected by voters, a Berkeley environmental group is continuing its long-running battle to drain Hetch Hetchy Reservoir, a linchpin of the water supply for 2.6 million Bay Area residents from San Francisco to San Jose to southern Alameda County. The reservoir in Yosemite National Park, built in 1923, violates California’s constitution, according to a lawsuit from the nonprofit group, Restore Hetch Hetchy, because the constitution requires water to be diverted in a “reasonable” way, and there are other places to store Hetch Hetchy’s water that aren’t in a national park.