<p>Post-Sandy cleanup includes an ongoing assessment of drinking water safety and a number of tri-state communities are now under a boil water advisory. Everyone across New York City, the northern suburbs, Long Island and New Jersey are urged to both preserve water and to take extra precaution by boiling tap water, experts said. Flood waters contaminated with bacteria, waste and other filth can seep into aquifers, pipes and wells, allowing contaminants to invade otherwise purified water.</p>