It's not just lead that could be lurking in your drinking water: Try chemicals that have been linked to cancer and other adverse health effects.

According to new findings from the Harvard T.H. Chan School of Public Health and the Harvard John A. Paulson School of Engineering and Applied Sciences, potentially dangerous chemicals called PFASs (polyfluoroalkyl and perfluoroalkyl) are above government-recommended safety levels in the drinking water of 6 million Americans around the country.

The research was published Tuesday in Environmental Science & Technology Letters.

PFASs, a group of man-made and organic compounds, have been used for more than 60 years in the manufacturing of industrial and commercial products like food wrappers, clothing and pots and pans. While some major manufacturers have stopped using certain types of PFASs, these chemicals persist in the environment, making their way into both people and wildlife.

"... The actual number of people exposed may be even higher than our study found, because government data for levels of these compounds in drinking water is lacking for almost a third of the U.S. population – about 100 million people," study author Xindi Hu said in a statement.

The researchers examined six types of PFASs in drinking water using more than 36,000 water samples collected by the U.S. Environmental Protection Agency between 2013 to 2015; they also co-located drinking water samples and point sources (like wastewater treatment plants, industrial sites and military fire training areas) and analyzed "the relationship between having point sources in the same watershed and the PFASs contamination in drinking water," according to Hu. They discovered PFASs at the minimum reporting level required by the EPA in 194 out of 4,864 water supplies spanning 33 states. What's more striking is that in 66 of the public water supplies studied (that 6 million people count on), at least one sample met or exceeded the EPA's safety limit of 70 parts per trillion (ng/L) for two types of PFASs.

Exposure to PFASs has been linked in epidemiological studies to cancer, elevated cholesterol, obesity, hormone issues and immunosuppression, Hu said.

"These compounds are potent immunotoxicants in children and recent work suggests drinking water safety levels should be much lower than the provisional guidelines established by EPA," study co-author Elsie Sunderland said in the same statement.

The next step of this research will be to examine the potential health consequences of drinking the contaminated water, like hormone disruption, Hu says.