SasoChicken

Yeah, but I wanted the water just to be non-killing. That how the map I played on was: you could walk around on the sand underwater and not die (at least in a certain boundary)

Setting a grid to 1.7 coordinates in height is the lowest a player can survive in most of the water on Forge World. The coordinates for other objects depends entirely on their thickness, but since a grid is infinitely thin, that [1.7c] is the actual level at which the death barrier starts. All vehicles can survive at a slightly lower level then humans so an underwater plane can be lowered to a point where only vehicles will survive.