I can see how they'd have faked it. All you have to do us stop the video when the chap gets to the curve of the jump, then when he's out of shot, continue a pan. Add in a CGI in a person flying through the air, and finally have someone hiding in the pool to make the splash and appear.
After all, it would be very easy to get something like that wrong - and the pool is too small for a safe landing.
Even so, enjoy!
Now that's my kind of water slide!
[Edit: It seems to be part of a German advertising campaign for Microsoft Project.]