Calorific value

[NewDazzler]

I was recently asked the following question "How many calories are there in a glass of water?"

Although I answered the question in the quiz with the expected answer of zero, I got to thinking, surely since the calorie is a unit of energy, then a glass of water does contain calories,  just not in a form usable by the human digestive system. Like saying cellulose has no calories because we can't digest it, but to a rabbit for example it's full of them, any comments ?

[Didwot]

A calorie is the amount of energy required to raise the temperature of one cc of water through one degree celcius. If you know the size of the glass and the temperature of the water (above absolute zero) you can work it out. Food values are given in kilocaleries (one thousand calories) but these are also referred to as "calories" or large calories just to make life difficult.

[rojash]

The calorific value of food is the amount of energy released when it is digested or burnt, so water has zero calories.

Didwot's answer is correct insofar as it tells you the value of a calorie, but it does not contain anty information which would allow you to calculate the calorific value of water.

[Didwot]

Ah but the question was;
"How many calories are there in a glass of water?"
Not
"What is the calorific value of a glass of water?"
NewDazzler was pondering if it was a trick question.

[jake-the-peg]

Of course the calorific calculation always assumes that the energy must be liberated chemically.

If you liberated the energy in a fusion reaction the answer would be lots!

But thats a rather contrived answer

[Space]

water doesnt containt any energy that your body can use. So from a nutrition point of view, it has zero calories.

However, if you drink cold water, your body will burn quite a few calories just to warm it up as it enters your body.
So for example, if you drink 250 ml of ice-cold water, it costs you about 9000 calories, or 9 kcalories.
So my answer is not "zero" but "minus several kcalories"

[rojash]

But of course, hot water will impart energy, so maybe the answer should be "depends on temperature"