Ancient civilizations in hot, arid climates used earthenware pitchers to chill water. An earthenware pitcher was filled with water, the temperature of which was initially the same as the air. After a few hours, the water was much cooler than the air. Here is how it worked: the porous earthenware allows water to diffuse through the walls. When the water reaches the surface, it evaporates. The evaporation draws energy from the water in the pitcher, which cools the water. The lower temperature is maintained because