I'd say Rock, then water. Then sand. Yes, the water gets cloudy, but there shouldn't be anything in it for another month anyway.
Maybe its useless but my thought was this way all the sand settles in the rock work well, but i guess that could be just as easy with the sand in dry and allowing you to move it all around and smush it into cracks... Either way, cloudy water is not an issue, but i suppose the order of things doesn't really matter now that i think about it