Ever the leader on environmental issues, California is moving ahead with a bill that would give it the nation’s most stringent bottled-water quality standards. Under the terms of the bill, bottled-water companies would have to include greater detail about contaminants on bottle labels, issue water-quality reports much like those produced by public water agencies, and, like those agencies, be subject to inspections by the state Department of Health. Makers of bottled water criticize the proposed legislation as unnecessary and costly, but backers note that 70 percent of Californians drink bottled water regularly, believing it to be cleaner and healthier than tap water — an assumption that isn’t necessarily true.