Cold water in rural India : matka(earthen ware)
Ok so here's a little insight into how water is cooled in the earthen pots used in rural India.Thes pots go by the name of "matka"and they have been in use in India since the Indus Valley Civilisation. Modern versions have a tap!!Trust me the water u drink from these pots is cold.Atleast a few degrees cooler than it would be if u kept the water in a plastic bottle without any refrigeration.
Here's wat i found out when i googled.(i daresay i could have explained but the language used here i think is clearer)
"A matka is made of mud and has many minute pores (extremely small holes). No matter how tightly you pack the mud, these pores remain. It is through these pores that the water, placed inside the matka, oozes out. Now, to evaporate, the water needs to absorb heat, which will change it to vapour.
The only way the water oozing out of the matka can turn to vapour is by absorbing heat from the liquid within the matka and the matka itself. Due to this process of continuous absorption of heat from the water inside the matka, in a few hours, this water becomes cool.
Glass and metal do not have any pores. So the water placed inside glass and metal vessels cannot seep out and evaporate. Therefore, the water inside remains hot."
source : www.pitara.com