I have lots of experience in Norway and lots of experience summer downhill skiing at Mt. Hood in Oregon.
I haven't seen waterskiing in Norway. I'm sure there are people doing it somewhere though! I imagine the high cost of gas and low temps might be why there's lots of kayaking, fishing, etc, but maybe not as much waterskiing/wake boarding.
Summer snow skiing is generally not that much fun unless you're into running gates or riding a terrain park. This is because the terrain is very limited and the hours where the surface is decent to ski on is very short. The snow will be frozen solid first thing in the AM and will be slushy by 11am or noon. If you go, I suggest arriving very early in the AM and buying the shortest ticket they offer. Two or three hours is plenty to say you've done it. I know that they offer summer skiing at Stryn, but I haven't been summer skiing in Norway, only Mt. Hood.