How do I make a room look like it is full of water?

[Zoanon]

I am setting up a skybox art gallery that is aquatic-based and want the rooms to be full of water. What can I do?

[Amethyst Jetaime]

You can't just put a water prim in it because when people are inside the prim it won't look like water. 

I would suggest you find some suitable animated water textures and apply them to the walls, ceiling and floor.  If you want anything to show beneath the water us use prims to cover the room and make them a bit transparent using the transparency setting under the texture tab in the edit tool box.  If you have the prims, put a transparent animated water caustic prim on the floor and ceiling, on top of the textured water.

I'd then use phantom transparent lighted prims and color the light blue. You can use one if the room is less than 20 x20 m.  Use a few if the room is larger or you would like to have varying light levels in a room.  I'd even perhaps use advanced lighting and a light texture that looks like undulations if enough patrons run there graphics with advanced light.

Turn a few swimming sea creatures loose to complete the effect.

[Nalates Urriah]

What you are asking for is volumetric environment control, or similar label. We don't have that in SL. May be SL2.

The closest we have is Windlight. Most of us know Windlight settings for our viewer. But, there are the same settings for parcels and regions. Unfortunately with Windlight the settings are controlled by the parcel boundary with no consideration for elevation.

Using fog and light you can create an under water like environment. But, it will extend from the ocean surface level in the region up to the sky (there may be an elevation at which Windlight stops, but I don't know. You can check Limits in the SL Wiki for limitations like that.)

The Firestorm Viewer had or has (I have forgotten - you can ask in Firestorm Support Group) a modified Windlight that allows different environmental settings via Windlight at various elevation ranges you can control. About 2/3's of SL  users run that viewer. If you use the Firestorm settings about a 1/3 of your visitors won't be able to see the correct environment.

Some nicely done artistic regions have a visitor staging area where the user/visitor is stopped and shown how to set their viewer's Windlight controls for the best viewing experience.

Unfortunately there is no BEST solution for what you want, only some work-arounds that partially work.

A feature like this has been requested many times over a long period of time. Apparently it was too complicated a feature to add to the current system. Don't expect this to change before the arrival of SL2.