You would think there would be plenty of ways to test how much marijuana is being used in a country. But apparently the only way to do so in Canada is through sewage.

As part of Canada's efforts to legalize marijuana, the country will begin testing sewage in six cities to determine how much cannabis is being used. Toronto, Montreal, Edmonton, Vancouver, Surrey and Halifax will all contribute samples from their wastewater treatment plants for the testing. The combined populations of these six cities is about a quarter of the country's total.

If you think testing sewage to determine drug use is weird, you're not wrong. But it is useful. Several countries in Europe as well as New Zealand and Australia test their sewage to determine how much drugs are being consumed by their citizens. It's a more scientific way to determine marijuana use, because other methods such as surveys suffer from low participation rates and possible inaccurate responses.

The hope is that these studies will determine how much cannabis is being used total in these cities, then subtract the number of legal sales in each to determine how much illegal marijuana is being sold and consumed throughout the country.

Of course, there are some issues with testing. Suburban residents may be purchasing and consuming their marijuana outside of major cities, but since they work in the major urban areas, their cannabis use could contribute to the city's sewage when they use the bathroom at work. Also, scientists right now can only test liquid wastewater to determine drug use, but most of the actual evidence of cannabis consumption appears in a more...uh..."solid" form. So the results may not be as entirely accurate if they were testing "non-liquids."

So if you live in Canada, try not to think about the government testing your urine the next time you go to the bathroom.

(h/t NPR)