Ngo Practical Action is working with communities to make zeer pots - very clever fridges made using clay, water and sand. They consist of two earthenware pots of different sizes, placed one inside the other. The space between is filled with damp sand that's kept moist by adding water, and the smaller pot is filled with food. The top is covered with a damp cloth, then as the water in the sand evaporates towards the outer surface of the larger pot, there's a drop in temperature of several degrees. This keeps the contents of the smaller pot cool. A zeer pot can keep 10kg of food fresh for up to 20 days.