Question

how does the water kept in an earthen pot become cool during summer​

Answer 1

because sandy soil has large water holding capacity

Answer 2

Water kept in an earthen pot become cool during summer because sand has pores between them and water seeps out and because of that water particles evaporate. The energy needed for evaporation is taken from the water kept in the earthen pot. continuous process of evaporation and seeping out of water makes the water cool.

note : Evaporation - When a liquid changes to a gaseous (or vapour) state without boiling.