A new study about cannabis use has flushed out surprising results.

In one of the first studies of its kind to utilize hard data rather than survey-based results, Dr. Dan Burgard and a team of researchers at the University of Puget Sound and University of Washington analyzed wastewater to understand how cannabis consumption has changed over the years. The team captured samples between the years of 2013 and 2016, evaluating how usage has fluctuated before and after the state’s 2014 legalization.

The way they collected these, err, samples is where things get a bit gross. The researchers used new methods to detect trace amounts of THC metabolites in the waste stream (i.e., whatever leaves your body and gets flushed down the toilet after you smoke, vape or eat cannabis.)

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In other words, the proof is in the pee.

“You can ask somebody with a survey, how much of this illicit drug do you use and you may or may not get the right answer,” Dr. Burgard told KING 5 News.

“With wastewater, it’s anonymous, and wastewater doesn’t have any reason to lie.”

Published in the journal Addiction, the results revealed cannabis use had increased in the area and moved away from the illegal market. The amount of THC found in the Puget Sound’s public wastewater coming from the Seattle-Tacoma region steadily increased nine percent per quarter, amounting to a doubling in weed consumption. The research team did also see a particularly large spike at the end of 2016.

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Dr. Burgard explained that his team’s research is part of an international study with 60-80 other cities around the world. As far as the data is concerned, he said, western Washington is a world leader in Cannabis, even over the city of Amsterdam.

This isn’t the first time he’s used this form of collecting data to learn about consumption of a particular substance. He previously studied how college students’ tendency to use “study drugs” like Ritalin and Adderall changed over the course of the semester. He found they increased eight-fold during finals, according to AP.

We know, we know. You’re shocked.

Brian Smith of the Washington State Liquor and Cannabis Board was also enthusiastic about the study, telling KING 5, “There’s been a lack of research on marijuana use because it’s illegal federally, and that has an impact on what people can really know… things like this are a step in the right direction.”

GreenState wondered how factors like longer showers and rainwater would allow the team of researchers to accurately compare use between cities. Burgard said they were among many accounted for the study.

Have comments on this article or questions about cannabis? Ask GreenState or send inquiries and tips to amanda.bartlett@sfchronicle.com