You turn on the tap and expect clean water. But what exactly is in that water? Analysts at EWG, a nonprofit environmental group, found a number of chemicals that are known to cause cancer. … EWG has a new tap-water database. Analysis of Los Angeles Department of Water and Power water found the level of arsenic 430 times its own EWG recommendation. It also found chromium at 29 times recommended levels, and acids from disinfectants at 184 times.