Drinking water treatment that pursues a multi-contaminant approach, tackling several pollutants at once, could prevent more than 50,000 lifetime cancer cases in the U.S., finds a new study by the Environmental Working Group. The finding challenges the merits of regulating one tap water contaminant at a time, the long‑standing practice of states and the federal government. In the paper, published in the journal Environmental Research, EWG scientists analyzed more than a decade of data from over 17,000 community water systems. They found that two cancer‑causing chemicals—arsenic and hexavalent chromium, or chromium‑6—often appear together in systems and can be treated using the same technologies. If water systems with chromium‑6 contamination also reduce arsenic levels to a range from 27% to 42%, this action could avoid up to quadrupling the number of cancer cases compared to just lowering chromium‑6 levels alone, the study finds.