Question

water kept in an earthen pot becomes cool in summer

Answer 1

When water is poured into the earthern pot, a small part of  the water poured exits through the pores on the pot and it evaporates from the surface of the pot, and thus making the water in the pot cooler than before. For evaporation to take place, water should get converted to vapour which occurs only when there is heat in the surroundings. So water evaporates when it absorbs heat making the container cooler. When the molecules escape the liquid a vapours, the water loses heat in the form of kinetic energy of the leaving molecules.

Answer 2

It is due to a phenomenon called evaporation . Earthern pots have many minute pores (holes) in it . The heat on the surface of water oozes through these pores and thus the temperature lowers .Thus the water becomes cooled !