Like a performing monkey you're asked to perform another trick and as luck would have it you happen to have your bottle of water and some rubber bands.
Show the bottle to be empty other than some water and that nothing is hidden under the cap.
Take a band off your wrist and you place it around the bottle.
With a wave of your hand the band penetrates the bottle and sinks to the bottom.
When your spectator(s) are done swearing and just before they threaten to burn you for the crime of witchcraft, hand them the bottle for examination.
Water Logged is a seemingly impromptu effect that is very easy to do and leaves your spectator with an impossible souvenir.