The method could help law enforcement identify new drug hot spots and monitor whether anti-drug measures are working, researchers said.
Kurunthachalam Kannan and Bikram Subedi from Wadsworth Center, New York State Department of Health, noted that to date, most methods to estimate drug use in the US are based on surveys, crime statistics and drug seizures by law enforcement. But much illegal drug use happens off the radar.
To better approximate usage, scientists have been turning to waste water. Like a lot of other compounds from pharmaceuticals and personal care products to pesticides, illegal drugs and their metabolic byproducts also persist in sewage.
In Europe, a number of studies have been done to see how well waste water treatment plants are removing illicit drugs from sludge before treated water is released into the environment. But until now, no study in the US had looked at this, likely leading to underestimates of abuse, researchers said.
Mr Kannan and Mr Subedi wanted to form a more complete picture of drug use, so they studied levels of illicit drugs at two waste water treatment plants in Albany, New York. The scientists found cocaine in 93 per cent of all untreated samples.
Levels of byproducts from opioids and hallucinogenic drugs were also detected. They found that the waste water treatment plants didn't remove all illicit drugs before releasing water back into the environment - and eventually into drinking water.
The researchers suggest, tracking drugs in waste water could help policymakers and law enforcement understand patterns of abuse and better fight it.
The study was published in the ACS journal Environmental Science & Technology.