Mythbusters did an episode similiar to that, although they were using compressed water in two liter plastic bottles(and it failed). That guy appears to have strapped a wave runner / jet ski on his back lol
Who cares if it is is a jet ski or really works? They important part is that it is super cool. The equipment will draw attention of the chicks on the beach thereby allowing you to use the rest of your equipment! Oh yeah, I want one