By Samantha Grossman
January 22, 2015

Bill Gates stopped by The Tonight Show Wednesday evening to talk about the Omniprocessor, a machine that aims to help sanitation issues in third world countries by turning human waste into drinking water — as well as electricity and clean ash.

Gates recently promoted the machine, which his foundation has helped fund, and shared a video of himself testing the water on his blog.

So naturally, the billionaire philanthropist decided to trick Fallon into tasting some of this “poop water” too. He sets up a taste test with two seemingly identical glasses of water and then invites Fallon to choose whichever one he wants. And then things get interesting.

MORE: Watch Bill Gates Drink Water That Had Been Poop Just Moments Before

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