Tests of the wastewater in seven unnamed municipalities in the U.S. have turned up quantities of several illegal drugs, scientists say.

The quantities of illicit substances, which are excreted through drug users’ urine, could potentially be used to determine how many people use the drugs in a particular area, Web MD reports.

Researchers at Oregon State University analyzed the wastewater in seven areas in the country and discovered that methamphetamine was the most commonly detected substance.

The findings, published in Environmental Science & Technology, also exposed concentrations of cocaine, ecstasy, MDA and ketamine – although none of these drugs was as widely present as meth.

According to the scientists, the Western and Southern regions of the country had the highest concentrations of drugs in wastewater, but they would not specify which cities.

Methamphetamine is a white, odorless powder that can be taken orally, snorted, smoked or via injection.

Short-term use can result in insomnia, overactivity, loss of appetite, breathing problems, irregular heartbeat and raised blood pressure. Over the long term, meth users may lose weight, suffer dental problems, feel anxiety, experience hallucinations and have violent behavior.