U.S. EPA has found 104 chemicals that might require regulations to keep them out of tap water -- the longest list of potential contaminants ever compiled by the agency.
A 1996 law requires EPA to evaluate possible tap-water pollutants every five years and make regulatory determinations for at least five of them.
The new list -- the agency's third -- includes pesticides, commercial chemicals, disinfection byproducts and, for the first time, pharmaceuticals.
"The thing that they did differently this time was they looked at a much bigger universe to start out with," said Mae Wu, a staff attorney for the Natural Resources Defense Council. "They kind of looked at every potential chemical that could end up in drinking water. It's a lot more extensive than the first two lists."
But the agency has yet to regulate a single contaminant that has appeared on any of the lists, Wu said.
"There are some flaws in the process," she said. "They just have to make a determination on five of them. That decision can be that they're not going to do anything about it."
The agency monitors 91 contaminants in tap water, with most chosen for regulation decades ago.
EPA said it evaluated approximately 7,500 contaminants for the new list, ultimately selecting 104 chemicals and 12 microbes based on their potential to pose health risks through drinking water exposure.
The agency said it will continue to research the contaminants and will determine by 2013 whether to propose drinking water regulations for some of them.