ZEER

A pot-in-pot refrigerator, clay pot cooler or zeer (Arabic: زير) is a non-electric evaporative cooling refrigeration device. It uses a porous outer clay pot (lined with wet sand) containing an inner pot (which can be glazed to prevent penetration by the liquid) within which the food is placed. The evaporation of the outer liquid draws heat from the inner pot. The device can cool any substance, and requires only a flow of relatively dry air and a source of water.