More than 200 million people are at risk of drinking tap water contaminated with chemicals that cause cancer, liver damage, birth defects and other reproductive harms, according to research released Wednesday that includes an interactive map of high-risk hot spots. The map, developed by the Environmental Working Group (EWG), focuses on arsenic, chromium-6 and nitrate. … Of the three chemicals examined in the report, nitrate affects the most people in terms of tap water. EWG said nitrate is affecting the tap water of an estimated 263 million Americans in 49 states served by 26,644 water systems.