Weird thing about water in 3D. It's not like you lay a big "box" of water material over a scene. Instead you play with the lights that illuminate the scene. You set them so it's like they are shining through fog or dust. You also place a "gel" over they light to simulate ripples in the water. And finally you set the light so that it fades off over a distance. The effect is very pretty and artistic. The example here is of a sort of free floating version. Actually the effect is even nicer if there's a sea floor or other set pieces.