We are completely aware that keeping water in earthen pots for a few hours makes the water cool and refreshing. Since our ancestors did not have our huge refrigerators to cool their water, they used this simple technique. Even with our modern, tough metal and glass containers, we cannot achieve this, so how does it happen? What makes the pot so special?

First of all, you need to understand the process of cooling. Physics explains this principle well - when evaporation takes place, cooling occurs. This is because for evaporation to take place, the water needs to change into vapor or gas and this only happens when there is heat in the surroundings. So when the water absorbs heat, it evaporates and this makes the container or surroundings cooler. The earthen pitcher contains many pores or small holes. When water is poured into the pot, a small part of it exits through these pores and evaporates from the surface of the pot, thus making the pot (and remaining water) cooler than before. Glass or metal jars cannot cool the water since they have no pores.