1. You better be wearing a life jacket before you end up in the water.
The gasp reflex in action (source: 3Nues)
Cold water forces a rapid, uncontrollable gasping in everyone and that lasts from 1-3 minutes. If you happen to gasp while your mouth is underwater, you will draw the cold water into your windpipe and lungs which can then spasm and contract. Even if you manage to get your mouth above water, you may still not be able to clear the water and get enough oxygen. If things go really wrong, your epiglottis may spasm closed and you will dry drown. (The epiglottis is the cartilage flap that keeps liquid out of your lungs when you drink.)
There is some evidence that keeping the cold water off your face and head may lessen the gasp reflex. That is why you want the life jacket on before you hit the water. It helps to keep your face and mouth out of the water. The initial immersion in cold water causes a sudden constriction of surface blood vessels which causes an immediate jump in blood pressure and heart rate; sometimes to maximum heart rate. If your heart cannot handle this jump, it stops and you die. This seldom happens in healthy and fit people but the danger is still there. If you have a choice, make sure to wear a life jacket that is self-righting so that it keeps your face out of the water if you are unconscious....