Solution

Pot surface made of earthen clay have a large number of pores over its surface.

Evaporation is a process when a liquid molecule loses its energy and converts to the gaseous molecule. This is what happens to water inside the pot.

The liquid molecule which will be having the highest energy level among the pot water will convert into a gaseous molecule first. So what will be left behind in the pot water, that will be the molecules of water having lesser energy? If this process keeps going on for hours, subsequently the water in the pot will turn into a colder one.