I am building a structure that will be half in the water and I want to make the area that is in the structure without water, how can I do it?

Look into visareas: http://freesdk.crydev.net/display/SDKDO ... nd+Portals
They are a bit buggy though, so you still get splashes where the water surface would have been sometimes.

You could also use the river tool to make a water surface. I think theres also a better way to make an water surface (btw with underwater and everything). ill have a look.

Greetings

I assume you're thinking of a water volume. Yes that should work.