Floating Islands are currently a true mystery, and no one really knows why it happens. The water mainly comes from the ring of storms, so it's not inexhaustible, per say. Droughts have occurred in the past, when the water reserves were running low.

Now that there is an easy way to get down to sea level, I would say that the droughts aren't as dangerous anymore, and there would likely be a roaring business in desalination.