How come I've never thought of this before? What if someone were to use this as a revenge tactic? Instead of water, a barrel of oil or can of gasoline. Poke a hole in the barrel or can, superglue a fuse to plug up the hole, and rig it so that a match automatically stikes and ignites the fuse? Bam! Homemade bomb for $10-$20 depending on amount of gas. To make the match strike itself just buy a cap gun and tie the trigger to string and tie that to the doorknob. Soak the match in gasoline the day before so it is dry and will burn quicker.