Do not drink more than one percent (1%) of your body weight in ounces of water at a time, it may make you very sick because your stomach will get caught off guard with the surplus of unexpected water. (150 lbs = 24 oz)
Don't push it. If you hold your breath for too long, you may suddenly gasp and suction the water down your trachea into your lungs.
NEVER have a water chugging contest.
Never chug water when laying down. It could make you choke, and you could be injured or die if it goes down the wrong tube.