you dont have to book for the waterpark, although it ll be packed i would imagine in teh Summer holidays so go early on to get a good sunbed. The price when we went in May was 30 ytl each hope this helps enjoy we did !!!
We paid £12 last week, we went to the water part on the mountain above McDonalds, i was not impressed, they had 6 water slides and the pools were filthy.
We have been to the new water park, there are 9 slides, there are some pictures i put on the forum somewhere i am not sure how to link them up but as you can see it looks clean, we also went to the Atlantis one and walked out after a couple hours as we thought it had gone down over the years and looked really dirty, but i suppose everyone has there difference views
They do have 9 slides, 4 of them are the same (joined together straight drop slide's) and one of them was out of order.
If it is smaller children you are taking they will probably enjoy it, we had a 7 year old with us and he loved it, if your kids are a bit older they will be bored within the hour.