Ms. Jackson announced her intent to review the nation’s drinking water standards a year ago, ordering an extensive review of the health effects of perchlorate and other toxic substances found in city water supplies. She announced on Wednesday that her agency would set standards for as many as 16 other toxic and carcinogenic chemicals.

The agency said it would take three or four years to complete the regulations.

“While we’ve put in place standards to address more than 90 drinking water contaminants,” Ms. Jackson said Wednesday in testimony before the Senate Environment and Public Works Committee, “there are many more contaminants of emerging concern, which science has only recently allowed us to detect at very low levels.”

Perchlorate can occur naturally, but high concentrations have been found near military installations where it was used in rocket testing and around places where fireworks, flares and solid propellants are made. Researchers have found that it may impair the functioning of the thyroid, potentially stunting the growth of fetuses, infants and children.

The military contractors who use the chemical have balked at tighter regulation, saying that substitutes are more expensive. But environmentalists and officials of some municipal water services have been calling for years for tighter rules on perchlorate and a number of carcinogenic chemicals, including industrial and dry-cleaning solvents.

The environmental agency has found measurable amounts of perchlorate in 26 states and two United States territories that it says could contaminate the drinking water of anywhere from 5 million to 17 million Americans. The Food and Drug Administration found the substance in more than half the foods it tested, and health researchers have found traces of it in samples of breast milk.