You cannot taste them. You cannot see them. But scientists say they are there: traces of prescription drugs in the water that comes from many people's faucets.
"Everything from antidepressants to heart medication to birth control pills to caffeine" has been found in certain drinking water, said Dr. Brian Buckley, environmental scientist at Rutgers University in New Jersey.
In his lab in New Brunswick alone, Buckley has found acne medication, barbiturates, caffeine and birth control medication in the water system.
While most of the medicines we take are absorbed by our bodies, he said, traces do escape via human waste and are flushed into our treatment plants, winding up in the water supply.
While the long-term health risks are unclear, there is evidence that medicines in the water, as well as hormones and chemicals, have negatively affected frogs and fish.
"The concern is we don't know what these chemicals do in the body over a lifetime of exposure," Buckley said.
Utility companies say that medicines can be found in the drinking water, but at levels so low that there is little danger. They say the only reason people even know about it now is because the technology has been developed to detect minute traces.
"One could safely consume 50,000 glasses of water a day without any adverse health effects," said Alan Roberson, director of security and regulatory affairs at the Denver-based American Water Works Association, which advocates for improved water quality and supply.
Even though the traces are minimal, Buckley warns that it is possible there may be potential hazards associated with long-term exposure to small compounds over one's lifetime.
"It is probably better to be safe than sorry," Buckley said. "And, in addition, there may be drug-drug interaction, even though the concentrations are very low."
While the government does not require water treatment plants to test for pharmaceuticals, there was enough concern to justify Congressional hearings in September to discuss emerging contaminants in U.S. waters.
"I am very concerned," said Rep. Carolyn McCarthy, D-N.Y. "We don't know for sure if it's having an effect on human beings and that's what we're trying to find out."
Some researchers, like Buckley, say it's necessary to investigate the water supply; if prescription drugs take action on the body in pill form, they're likely to have some effect when absorbed through another medium like water.
There are ways to protect oneself. ABC News asked researchers to test a widely available water filter for the home. They found it greatly reduced the traces of drugs in the water.
And communities across the country are creating drop-off locations where people can bring expired drugs to be incinerated, preventing them from ending up in rivers and streams and contaminating the water supply.
"I used to flush unused Ibuprofen down the toilet rather than have my small children consume them," said Kirsten Calia, a mother from Connecticut. "But now I know that there are great environmental ramifications to this."