Water kept in an earthen pot (matka) becomes cool in summer primarily due to evaporation through the pot's porous walls. The pot has many tiny pores allowing small amounts of water to seep out and evaporate from its outer surface. This evaporation process requires heat, which is absorbed from the water inside the pot itself, causing the water temperature to drop and making the water cool. Additionally, the clay material of the pot acts as a thermal insulator, slowing heat transfer from the hot outside environment to the water inside, helping maintain the cool temperature.
How it works:
- The evaporation draws latent heat from the water inside, reducing its temperature.
- Clay walls are porous, allowing seepage and evaporation, but are also poor conductors, providing insulation.
- The continuous evaporation process balances heat flow so water remains cooler than the external air.
- This natural cooling effect is similar to how sweating cools the human body by evaporating moisture and absorbing heat.
This is why traditionally in hot regions, water in an earthen pot remains pleasantly cool during summer without any external refrigeration.