Under 15-45 Min. Survival in cold water depends on many factors. The temperature of the water is only one. Others include body size, fat, and activity in the water to name a few. Large people cool slower than small people.
Fat people cool slower than thin people.
Children, because they are small, cool faster than adults. By swimming or treading water, a person will cool about 35 percent faster than if remaining still. Because the head is an area of high heat loss, drownproofing will cause a person to cool about 80 percent faster than if he kept his head out of the water. Drownproofing thus reduces survival time by nearly one half in cold water. This survival time can be increased considerably by getting as far out of the water as possible and covering the head.