I haven't been to Europa, but am planning on heading there in April of this year and will (like you) be headed for the Black Forest in addition to the theme park on the trip. I've done some research and, to be honest, there aren't really any decent theme or water parks close to Europa, which is a shame. The most reasonable is Holiday World (ie - Expedition GeForce) - but even that is 2 1/2 hours away by car.
I've heard rumours in the pipeline that Europa are planning to build their own waterpark at some point in the not too distant future - it'd no doubt be a welcome addition if built.
So, no, sorry. I'm sure three days at Europa itself wouldn't be too
much of a stretch though. Assuming it'll be your first visit?