The announcements come amid growing complaints that systems across the nation are delivering tap water that poses health risks to residents. Government and other scientists have identified hundreds of chemicals that are linked to diseases in small concentrations and that are unregulated in drinking water, or policed at limits that still pose serious risks.

In some instances, laws are sufficient, but they have been ignored: More than 20 percent of the nation’s water treatment systems have violated key provisions of the Safe Drinking Water Act over the last five years, according to an analysis of federal data by The New York Times. And the other major water law — the Clean Water Act — has been violated more than half a million times, though few polluters were ever punished.

To correct such lapses, the E.P.A. intends to reform agency policies that essentially require regulators to examine pollutants one at a time. Those adjustments will allow government scientists to evaluate large groups of similar contaminants at the same time and to issue new rules that apply to dozens of chemicals.

“This is a dramatic change in how we think about regulation,” said Cynthia C. Dougherty, the director of the agency’s office of ground water and drinking water. “We’ll be able to move much faster and issue stronger rules.” The agency previously announced it was developing plans to crack down on polluters and force water systems to abide by cleanliness laws.

Image Lisa Jackson, the E.P.A. administrator, said it planned stricter regulation of four cancer-causing chemicals. Credit... Cliff Owen/Associated Press

“We lost the public over the past decade by moving slowly and focusing on solitary contaminants that most people have never heard of,” said Dr. Pankaj Parekh, director of the water quality division for Los Angeles. “This will help us talk about health impacts, rather than long, complicated chemical names.”