It isn't...however, the principle is that there is energy needed to cool it down to body temperature and this will burn calories (same reason to drink cold water, bring it up to body temperature). Another theory is that cold water causes cramps so after exercising, the hot water is better. This is more nonsense. The only thing you need to worry about is to drink water as part of a good diet (along with eating well and exercising).

the is little or no difference in hot and cold water. you will do nothing but burn your tongue.