The test wouldn't be used to finger any single person as a drug user. But it would help federal law enforcement and other agencies track the spread of dangerous drugs, like methamphetamines, across the country.

Oregon State University scientists tested 10 unnamed American cities for remnants of drugs, both legal and illegal, from wastewater streams. They were able to show that they could get a good snapshot of what people are taking.

"It's a community urinalysis," said Caleb Banta-Green, a University of Washington drug abuse researcher who was part of the Oregon State team. The scientists presented their results Tuesday at a meeting of the American Chemical Society in Boston.

Two federal agencies have taken samples from U.S. waterways to see if drug testing a whole city is doable, but they haven't gotten as far as the Oregon researchers.

One of the early results of the new study showed big differences in methamphetamine use city to city. One urban area with a gambling industry had meth levels more than five times higher than other cities. Yet methamphetamine levels were virtually nonexistent in some smaller Midwestern locales, said Jennifer Field, the lead researcher and a professor of environmental toxicology at Oregon State.

The ingredient Americans consume and excrete the most was caffeine, Field said.

Cities in the experiment ranged from 17,000 to 600,000 in population, but Field declined to identify them, saying that could harm her relationship with the sewage plant operators.

She plans to start a survey for drugs in the wastewater of at least 40 Oregon communities.

The science behind the testing is simple. Nearly every drug -- legal and illicit -- that people take leaves the body. That waste goes into toilets and then into wastewater treatment plants.

"Wastewater facilities are wonderful places to understand what humans consume and excrete," Field said.

She said that one fairly affluent community scored low for illicit drugs except for cocaine. Cocaine and ecstasy tended to peak on weekends and drop on weekdays, she said, while methamphetamine and prescription drugs were steady throughout the week.

Field said her study suggests that a key tool currently used by drug abuse researchers -- self-reported drug questionnaires -- underestimates drug use.

"We have so few indicators of current use," said Jane Maxwell of the Addiction Research Institute at the University of Texas, who wasn't part of the study. "This could be a very interesting new indicator."

David Murray, chief scientist for U.S. Office of National Drug Control Policy, said the idea interests his agency.

Murray said the U.S. Environmental Protection Agency is testing federal wastewater samples just to see if that's a good method for monitoring drug use. But he didn't know how many tests were conducted or where.

The EPA will "flush out the details" on testing, Benjamin Grumbles joked. The EPA assistant administrator said the agency is already looking at the problem of potential harm to rivers and lakes from legal pharmaceuticals.

The idea of testing on a citywide basis for drugs makes sense, as long as it doesn't violate people's privacy, said Tom Angell of the Students for Sensible Drug Policy, a Washington-based group that wants looser drug laws.

"This seems to be less offensive than individualized testing," he said.