Yes, there are towel for rent at the water parks. Can't remember how much they cost. Not very much, I think you get some of the money back when you turn them in. Then, there are alway the ones for sale in the gift shops as well.
uhm so i can bring my own ones....do i then have to bring the ones i brought from at home or can i take the ones from the hotel ? from the hotel pool ?
You can bring your own. Most hotels don't like you to take their towels off property, but I have seen people do it. It is much more convenient to just rent towels at BB or TL, then you don't have to carry them around or wash/dry them afterwards!
I've always brought towels from the hotel to the waterpark. I believe that is acceptable. Almost everyone there has the plain white towels from the hotels as the ones for rent have a stripe, if I remember. I figure, all towels go to a central laundry facility so the hotel is not "losing" their towels.