If you sit in the front you may get pretty wet. The back is really not that bad at all. I stayed pretty dry in the back.
Disney uses a lot of effects to make the splash look worse than it is...like water cannons shooting just as you hit bottom. You will get some water on you no matter what. Ride during the hottest part of day then you will dry quickly. Or, ride Space mountain right after and the fast ride will dry you off