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NIDA. (2019, September 23). Drug Use: It's in the Water. Retrieved from

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The NIDA Blog Team
September 23 2019
A test tube getting a sample from a pond
©Shutterstock/Irina Kozorog

You probably know that scientists can test your urine to see if you’ve used a drug. Drugs break down into chemicals called metabolites in your body—so what scientists see in the lab isn’t the actual drug, but proof that the drug was recently in your system.    

Did you know that the same kind of testing can help officials measure how much drug use is going on in a large population?

They do this by studying wastewater—the water that goes from homes and businesses into the sewage system.

What can we learn from testing wastewater?

Researchers can measure metabolites in wastewater to get an idea about a population’s general drug use, their use of particular drugs, and more.

Analyzing chemicals in a population’s urine can reveal a lot about overall drug use in a geographic area. For example, researchers partly funded by NIDA recently examined wastewater in Washington state, which has legalized marijuana for adults, with sales beginning in 2014.

One goal of the study was to see if legalizing marijuana affected how much the drug was used in the state.

The researchers analyzed samples from public wastewater in part of Washington state for the metabolite THC-COOH. (THC is the chemical in marijuana that causes the user’s “high.”) They found that within the 3-year period of their study, marijuana metabolites in the wastewater doubled, suggesting increased use.

How do officials use this information?

Wastewater testing is only one possible measure of marijuana use. Other measures might be sales, or surveys and reports from health officials.

Wastewater testing does not reveal anything about specific people and their drug use, or how old the users are. But it could help officials to spot changing trends in drug use. They can then use that information to alert hospitals about new drugs being used in their area, and predict if new types of drug treatment may be needed.

Learn more: The facts about drug testing for teens.