Having trouble with your bottle jugs collapsing when you put them in the water? Try this simple and effective trick. Place the opened empty jug in your freezer and leave it for an hour or so until it is thoroughly chilled. Cap it tightly immediately on removing it from the freezer and you are good to go. It works on a commonly known principle that air condenses when chilled. With the cap on tightly, the air inside expands when removed from the freezer and you have a tight bottle that will stay tight, even in cool water.