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.

How evaporation causes cooling in earthen pot?

Solution: When we kept water on the earthen pot (matka), the water molecules evaporate from the several tiny pores of the pot. During this process, it takes the heat from the water and thus the water cools down due to the loss of heat. This is the reason why water kept in earthen pot keep cool.

Does clay keep water cold?

When water changes to water vapour without boiling, it is known as evaporation. All clay products are made of mud. It naturally has many tiny pores (extremely small holes). ... Thus, it cools the water in the bottle / pot.