Water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients.

Does water really have no calories?

Plain water is calorie-free. Calories come from three nutrients in your diet — carbs, fats, and proteins. Alcohol — while not considered a nutrient — contributes calories as well. Plain water is devoid of these nutrients and thus contains no calories.

Can something actually be zero calories?

The FDA legally allows manufacturers to label anything with less than five calories as having zero calories. (For example, the "No Calorie Sweetener", Splenda, really has 3.4 calories per packet.)