An anonymous reader writes: In an exclusive report via The Guardian, investigators found there to be at least 33 cities across 17 U.S. states that have used water testing "cheats" in an effort to cover up potentially dangerous levels of lead. The investigation was launched after the toxic water crisis in Flint, Michigan, and found that 21 of these cities used the same water testing methods that resulted in criminal charges against three government employees in Flint. Such cities include Chicago, Boston, Philadelphia, Detroit and Milwaukee. The Guardian reports: "The Guardian investigation concerned thousands of documents detailing water testing practices over the past decade. They include: Despite warnings of regulators and experts, water departments in at least 33 cities used testing methods over the past decade that could underestimate lead found in drinking water. Officials in two major cities -- Philadelphia and Chicago -- asked employees to test water safety in their own homes. Two states -- Michigan and New Hampshire -- advised water departments to give themselves extra time to complete tests so that if lead contamination exceeded federal limits, officials could re-sample and remove results with high lead levels. Some cities denied knowledge of the locations of lead pipes, failed to sample the required number of homes with lead plumbing of refused to release lead pipe maps, claiming it was a security risk."