[clarencecuzz]

No, it's not possible to have water inside an interior. There is however an object id that resembles water and the water effect, however it is solid and can be walked over, still usable as water however. Most interiors are placed at very high Z co-ords, such as Liberty City for example. Therefore, if you were to create a water texture at that point, then nearly all of the GTA map would be under water. Not even sure if that's possible, but I would think not.