Earlier this year, Stats Canada wanted to figure out exactly how much cannabis was being consumed in the country so that they could gauge the size of the illegal marijuana market ahead of legalization. Normally, statisticians use polls to collect data, but since cannabis is still highly stigmatized, Stats Canada couldn’t rely on people being forthcoming about their cannabis use.

So instead of using the phone, the Stats Canada team turned to the nation’s toilets. From March through August of 2018, Stats Canada analyzed the wastewater of five cities: Halifax, Montréal, Vancouver, Edmonton and Toronto. Analysts tested sewage samples to detect amounts of THC-COOH — a metabolite produced by people after they consume cannabis’ psychoactive compound THC.

Here are the results.

Total Amount of Cannabis Consumed

Montréal topped the list in terms of the sheer amount of THC-COOH found in the city’s sewage. Toronto and Vancouver came in second and third respectively while Edmonton and Halifax were fourth and fifth. Of course, that doesn’t mean Montréal has more cannabis consumers than anywhere else in Canada because those high numbers of THC-COOH could be getting skewed by a handful of heavy consumers.