Under threat of a lawsuit from enviros, the U.S. EPA yesterday proposed strict new regulations that would cut by 90 percent the permissible levels of arsenic in tap water. Arsenic, which can cause cancer and other health problems, is currently found at harmful levels in at least 10 percent of the nation’s community water supplies. The EPA says its new rules, which would require upgrades in 6,600 water systems across the nation, could reduce the risk of cancer for 22 million Americans. Under the Safe Drinking Water Act of 1996, the EPA was supposed to have set a new arsenic standard by January 1 of this year, but its proposal was held up at the White House for review. Two weeks ago, the Natural Resources Defense Council threatened to sue unless the agency moved quickly to release a new standard.