By encasing the vessel containing it in a wet cloth and hanging it up in a draft out of the sun. The rapid evaporation of the moisture in the cloth extracts heat from the vessel and the water. In hot climates porous vessels are commonly used for this purpose. The water oozing through the earthenware keeps the outside damp, so that evaporation is continuous.
Air is cooled in a similar way in India by hanging grass curtains in doorways and sprinkling them frequently with water.