The jugs just sit on the top of the cover - and they are full or almost full, actually. So the solar cover is floating on the water, the jug is sitting on top of the cover, about 1 foot in from the edge. I used three while I was gone for 10 days, pump running, and the cover didn't budge. They might move a bit but I've not had one sink or anything. The water on top tends to accumulate by the jug, like if it rains, etc., and if it sits for more than a day or two it can get scummy...