Solving a 40-year mystery, scientists ID chemical found in millions of Americans’ tap water

For more than four decades, scientists have noticed a mysterious chemical in the treated drinking water of millions of people in the United States, but no one’s been able to pinpoint exactly what it is – until now.

For more than four decades, scientists have noticed a mysterious chemical in the treated drinking water of millions of people in the United States, but no one’s been able to pinpoint exactly what it is – until now. The authors of a study published Thursday in the journal Science believe the chemical – which they named chloronitramide anion – is a decomposition byproduct of chloramine, a chemical that many treatment plants use to make water safe to drink. About 113 million people drink tap water that exposes them to chloronitramide anion, the study says. It’s not clear whether the byproduct could be harmful to human health, but the study authors say its properties are similar to those of other molecules that are toxic enough for the government to regulate them. And there is some precedent, the researchers say, for chemicals that are used to purify drinking water creating byproducts that the US Environmental Protection Agency must regulate because they are likely carcinogens. In the early 20th century, many public water systems started using chlorine in low levels to make drinking water safe. It solved a major public health problem that had plagued leaders for centuries by ridding the water of cholera and typhoid, deadly germs that can spread through drinking water. But it also caused its own health problems.