As the latest installment of its "Toxic Waters" series, the Times explores how of the 60,000 chemicals used to treat the public's water supply, just 91 are regulated by the federal government.
And no new chemicals have been added to the list created by the Safe Water Drinking Act since 2000. Most of the laws from the act, which was created in 1974, are also out of date.
"All told, more than 62 million Americans have been exposed since 2004 to drinking water that did not meet at least one commonly used government health guideline intended to help protect people from cancer or serious disease, according to an analysis by The Times of more than 19 million drinking-water test results from the District of Columbia and the 45 states that made data available."
"People don't understand that just because water is technically legal, it can still present health risks," Dr. Pankaj Parekh, who oversees water quality for Los Angeles, told the Times.
Chemicals such as arsenic and mercury, which can lead to a variety of cancers, and manganese, which is linked to Parkinson's disease, were found in municipal water supplies by the Times.
"There's growing evidence that numerous chemicals are more dangerous than previously thought, but the E.P.A. still gives them a clean bill of health," Linda S. Birnbaum, director of the National Institute of Environmental Health Sciences, told the Times, adding that these chemicals can live in body tissue for years before affecting people.
But at least one head of a city's water system was unfazed.
Though data show the Pensacola, Fla. water supply had several dangerously high levels of chemicals, it has not violated the Safe Water Drinking Act in recent years.
As the executive director of Emerald Coast Utilities Authority tells the Times: "If it doesn't violate the law, I don't really pay much attention to it."