Are you thinking about going to the water parks in the winter? Two notes:
1) Disney heats the water in the water parks, so it shouldn’t be too uncomfortable (until you get out of the water!).
2) Disney usually only has one water park open during the colder months of the year.
And, a bonus note about Disney World resort pools – they are heated too! (Though we’ve found that if your resort has multiple pools, one is usually warmer than the others!)