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medium.com/usaid-2030/the-of...-mali-629df444acb8

Clay pot coolers, also known as zeer pots, have been in use for centuries in many parts of the world and operate on a simple principle of passive evaporation. These storage devices, which operate without electricity, consist of two pots nested together with a layer of sand in between and covered with a wet cloth. As water evaporates from the surfaces of the device, evaporation cools the fruits and vegetables inside the pot.