CEDAR RAPIDS - A study raises new questions about the water coming out of the tap. Nearly 40-percent of drinking water in the nation's largest cities might contain prescription drugs. That's the water for 41-million people. Although the traces of drugs were small, it has some concerned about the long term effects.

In Cedar Rapids, the city's water comes primarily from the Cedar River. Many cities get their water from sources such as this. In Nevada, Lake Mead is the water source for much of the southwestern U.S. But a new report finds it also contains trace levels of birth control pills, steroids, narcotics, and more.

An associated press investigation found traces of drugs in the water supplies of 24 major metropolitan areas out of 62 major water systems it checked. All kinds of medications: from anti-depressants, to anti-biotics, to heart medicine.

"There is no way that having pharmaceutical drugs in the water supply is going to be of any benefit," said Dr. David Carpenter of Suny Albany.

So how did it all end up in the water? Our bodies don't absorb all of the medicine we take, so some of it is excreted and flushed into our sewers. Sewage treatment plants don't remove the drugs. The treated water then flows into rivers and lakes. Then to drinking water plants which typically don't screen for drugs. But can it harm you?

Scientists are seeing effects on animals, but have yet to make any connections to human illnesses.

"No studies have demonstrated any effects on human health," said Marjorie Powell, pharmaceutical attorney.

The pharmaceutical industry points out the levels of drugs detected in tap water are minuscule. And the EPA says, while it is concerned about the issue, the country's water is still some of the safest in the world.

If you're concerned about what's in the water, experts say you can buy a reverse osmosis water filtration system. Traditional water filters aren't designed to clear away drugs.