One important note, if you don't make this so one cube and terrain cover the entire field of view and instead decide to go with tiling terrains (you'll have to copy each g2h of the terrain to the corresponding cube of water) make sure that when you have everything in place select all the cubes of water, make them positive then group them. Otherwise you'll get these nasty grids making it look like the water is actually cubes instead of all one body of water.