Cooling through evaporation is a natural occurrence. The most common example we all experience is perspiration or sweat. As perspiration evaporates it absorbs heat to cool your body. The principle underlying evaporative cooling is the fact that water must have heat applied to it to change form a liquid to a vapor. When evaporation occurs, this heat is taken from the water that remains in the liquid state, resulting in a cooler liquid.

Evaporative cooling systems use the same principle as perspiration to provide cooling for machinery and buildings.