From Dr. Darden of HIT Jedi fame...
Originally Posted by Dr. Darden
When you drink chilled water, which is about 40-degrees Fahrenheit, your system has to heat the fluid to a core body temperature of 98.6 degrees. This process requires almost 1 calorie to warm each ounce of cold water to body temperature. Thus, an 8-ounce glass of cold water burns approximately 8 calories, or 7.69 to be exact. Extend that over 16 glasses, 128 ounces, or one gallon — and you’ve generated 123 calories of heat energy, which is significant. There’s real calorie-burning power in cold water.