Well, I've seen 2 threads in a row asking how to retrieve things that drop into water, and I bet there's more, so instead of having to "Delete All" of the object, which you can do if there isn't many of it, you can prevent it from happening entirely by placing the largest Grid possible right on top of the water under you building space. Your Welcome.
I don't think it was necessary to make a whole new thread to reply to another thread (or 2). This isn't Bungie.net However, I agree, if your building a map over water, you might as well have a grid to not only catch things, but also to align the objects better.