Can you use just the waterpark or must you also have a room?

I believe they sell just water park passes. Go to website for prices.

Room booking is not mandatory.

Yes.

You can get a day or half day pass

You can get a day pass..

Either way - day passes are available

Day passes, but check prices, and overnight stay is definitely a better deal!

You can just use water park. They have full and half day passes