If you fall into cold water, you can delay the effects of hypothermia and increase your chances of survival as follows:
Keep as much of your body out of the water as possible. If you can, pull yourself out of the water onto a floating object.
The more energy you use in cold water, the more your body cools. If you can't climb out of the water, conserve body heat by staying as still as possible and reducing the body area exposed to the water. Protect your critical heat loss regions: head, sides, armpits and groin. Don't try swimming unless shore, or an object you can get onto, like an overturned boat is nearby and you can definitely get to it.
If you are wearing a lifejacket, you may be able to use the Heat Escape Lessening Posture (H.E.L.P.) to reduce heat loss: hold your arms tightly against your sides and across your chest, hold your legs together and up toward your chest.
In the case of two or more people wearing life-jackets, huddle together to conserve body heat and increase your visibility for rescuers.
(Olivia Rose-Innes, Health24, updated January 2012)