We had the same problem when Willy adopted us.

I always have a glass of water on the nightstand at night. After getting drenched 2 or 3 times -- such a rude way to be awoken -- I got a water bottle with a screw on lid. Willy still knocks it over in the middle of the night once in a while, but I don't get wet.

We're not big soda drinkers, but I started buying Diet Coke in bottles for the same reason.

But, Willy has now graduated to knocking over flower vases Haven't solved that one yet. Our dining room table chairs are water stained. I was going to re-cover them but why bother -- until he grows out of this new habit.