Bill Gates has been on a campaign to bring attention to efforts to process sewage into drinkable water. Earlier this month he took a sip from water processed by the the OmniProcessor, designed and built by Janicki Bioenergy, an engineering firm north of Seattle, that takes human waste and turns it into clean drinking water, electricity and clean ash.
And he took it a step further last night on The Tonight Show, challenging Jimmy Fallon to a taste test between bottled water and “poop water,” during an appearance to promote the publication of the 2015 Gates annual letter.
But there was a surprise twist. Watch the full video above to see what happened.