"A major goal of our work is to identify these chemicals and the reaction pathways through which they form," said Julian Fairey, an associate professor of civil engineering at the University of Arkansas.

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.

A newly identified chemical byproduct may be present in drinking water in about a third of U.S. homes, a study found. Scientists think it might be toxic but do not yet know.