A pot-in-pot refrigerator or zeer (Arabic: زير‎)

A pot-in-pot refrigeratorRefrigerate foods without using electricity -this mode of refrigeration goes back at least 5000 years.

It uses a porous outer earthenware pot, lined with wet sand, contains 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 be used to cool any substance.

Have any of you tried this.
More info – http://en.wikipedia.org/wiki/Pot-in-pot_refrigerator