The new study, which was be released in January in the journal Environmental Pollution. Conducted by the Environmental Protection Agency, it is the largest study of water coming out of wastewater treatment plants.

It looked at samples from 50 large-size wastewater treatment plants nationwide and tested for 56 drugs including oxycodone, high-blood pressure medications, and over-the-counter drugs like Tylenol and ibuprofen. More than half the samples tested positive for at least 25 of the drugs monitored, the study said. High blood pressure medications appeared in the highest concentrations and most frequently.

“We were surprised to find that many drugs occurring across all the wastewater plants,” said Mitchell Kostich, the EPA research biologist who led the study. “We were also surprised to see so many drugs of a particular class—the high blood pressure medications—appear at those levels across the board.”

many drugs, which we know are in the water, are not removed by reverse osmosis