WATCH: Justin Bieber fell flat on his BUM during his Purpose gig

Justin Bieber found out the hard way that splashing water on stage during a dance routine is a recipe for disaster.

The singer was in the middle of a song, and as fake rain flooded the stage, he fell right on his arse.

The moment was captured on social media and has been making its way around the Internet all morning.

As he slipped back, fans were heard gasping and asking if he was OK, but ever the, erm.. professional, Justin hopped back up and continued performing.