A botijo or búcaro is a traditional Spanish porous clay container designed to contain water. The botijo has the property that once filled and placed in the sun, it cools the water that it contains.
The botijo has a wide belly and one or more mouths where it is filled and one or more outputs called pitón o pitorro to drink from. The botijo is a typical element of Spanish culture and may vary in shape, color and material.
The operating principle of the botijo is as follows: the stored water is filtered through the pores of the clay and in contact with the outside dry environment (characteristic of Mediterranean climate), it evaporates, producing a cooling (2.219 kilojoules per gram of evaporated water). The key for cooling it, is by the evaporation of bleed water, as the water evaporates, it extracts thermal energy from the water stored inside the jug (and from the environment itself too).