KRON/CNN—Millions of Americans may be drinking water with unsafe levels of chemicals in it.

That’s according to a new Harvard University study showing at least 6 million Americans are drinking water with that has a man-made chemical known as PFAS.

California and 12 other states accounted for more than 75 percent of the findings and California was the worst.

PFAS’s are used to make things such as food packaging and non- stick cooking pans.

Some manufacturers are phasing it out, but researchers say because the chemical was used so heavily in the past that it has made it into the drinking water supply.

It has been linked to health problems including high cholesterol, obesity, and even cancer.