Is it possible to make water actual liquid not just a moving texture thing?
Yes, and there are many different ways of achieving liquid water but I think the most common approach would be to use point particles which you plug into to a marching cubes algorithm to generate the triangles through the scalar field the particles make up.
Each particle would repel other particles a bit while still attracting them somewhat to get a fluid stickiness. You'd have to heavily optimize it and work on a rather limited set to be able to run this realtime.
To finally give the generated mesh some water feeling you'd probably want to add some sort of water refraction shader.
You'll have to scour google for more information about implementing the various steps.
You can make realistic water in your favorite 3D app and export it as an .fbx with animations baked. Import into Unity and hit play (make sure play automatically is checked)...otherwise, you need a script to access the actual animation.
and it's best to name them like this: water@idle (these can be .fbx files, Maya files, or 3ds Max files...and other 3D apps too) water@splash (these can be .fbx files, Maya files, or 3ds Max files...and other 3D apps too) water@drain (these can be .fbx files, Maya files, or 3ds Max files...and other 3D apps too) etc
Hope this helps.
Shawn
Going by the room flood comment... Not going to happen, or easily I should say...
Check out: http://www.youtube.com/watch?v=QECUbMEIxhw
It's not with Unity, but you get the same response.... Water will have to be done with shaders for the look... As for actually moving, as Shawn said, you're going to have to model it actually coming out of the water, in to the room, and "flooding" it... It's not going to be an easy scripting job... On top of that, realistic water is very complex, and being so, it might be more than the 65000 (I believe that's the max) limit of polys... The best way to get around the block is to think of weird ways to bypass it... Maybe someone else'll post a way to do this, but doubt it...
Good luck though none-the-less!
The particle system have a function particle collider use that to do the liquid