I've heard that ice water thing, and have to wonder if it's just psychological. Now my curiosity is piqued.
Let's see. A Calorie (capital C, aka a kilocalorie) is the energy unit for food. It's also the amount of energy it takes to heat one thousand cubic centimeters of water 1 degree Centigrade.
Let's say you drink water that is very nearly frozen, at 0 degrees Centigrade. The relevant question is "How much energy do you burn over normal water?"
Let's say room temperature (and thus room temperature water) is 70F, or 21C. Then you're heating that water an extra 21C versus drinking normal water.
A 16oz water bottle is ~470 cubic centimeters in volume, so let's say you drink 3 of those per workout.
Then you are heating ~1500cc of water an extra 21C. That's 31500 calories (little 'c'), which is 31.5 Calories (kilocals.)
I guess it comes down to how efficient the body's methods of generating heat are, because if it's 100% efficient that's basically no calories at all. But it's unlikely that the body is 100% efficient at converting its energy stores to heat. Let's say it's 33% efficient -- that would be about 100 extra Calories per workout you'd be burning. I have no idea if 33% is the right number, though.
And that's if you're drinking 3 full 16oz water bottles that are, literally, ice cold.
That's also above the amount you burn for normal room temperature water, which is another 24 Calories, base.
In sum, if your body were 100% efficient at generating heat from energy stores, drinking three 16oz water bottles full of ice-cold water (32F, 0C) would burn 55 Calories.
If anyone has any idea of the body's actual efficiency (or probably efficiencies, I'm sure it differs depending on where it's getting the energy) at generating that heat, I'm curious now.
I always assumed this was just a myth, but if the body's not super-efficient at making heat, that could actually consume some relatively serious calories.