The video above demonstrates one variation of this basic cooler. As the wet sand evaporates, it removes the heat from the inner container, lowering the temperature.
As MixCat.com’s video shows, the temperature starts to drop pretty quickly, but it may take some time for the zeer pot to get really cold. In six hours, the interior went from 30 degrees C to 11 degrees, while the temperature outside was 35 degrees.
This DIY project is great to have in case your electricity goes out or for keeping your beer cool in the sweltering heat (the hotter it is, the faster the evaporation and quicker the cooling).