Matki (earthen pot)

A matki or matka in South Asia is an earthen pot used as a home "water storage cooler". It has been in use since ancient times and can be found in houses of every social class.

Production

They are made by the combination of two types of clay: the first is taken from the surface of the earth and the second after digging more than 10 feet deeper into the earth. Making a matka is a long process of at least 8 days. The clay is mixed with water, shaped, finished, polished, dried and fired in a kiln for 5 days.
Modern designs are fitted with taps.

Cooling process

The cooling process works through evaporative cooling. Capillary action causes water to evaporate from the mini-pores in the pot, taking the heat from the water inside, thus making the water inside cooler than the outside temperature. Hence it is used only during summer and not in winter.