The botijo generally has a wide, spherical belly with two openings on top -- a wide opening to pour water in the jug and a smaller drinking spout -- as well as one or two handles to carry it. Traditionally, people drink the water directly from the botijo by holding it up and tilting it so that the water pours from the drinking spout.
Botijo-etiquette demands that the lips do not touch the drinking
spout, as the water container is usually shared among several
people. The large opening is covered with a cork or a cloth after
filling the jug, in order to keep insects out. Botijos come in
different sizes, but on average it contains about 3 liters of water,
with larger ones holding up to 7 liters, enough to supply a small
group of people with drinking water for a full day.
After the botijo is filled with water, it is preferably placed
outside in the shade, although it also works when placed in the sun
or indoors. The technology is based on evaporative cooling, the same
process that keeps the human body cool by sweating. Because the
ceramic jug is not completely water-tight, a small amount of the
stored water filters through the pores of the clay and evaporates
once it comes in contact with the outside, dry environment.
Evaporation (the transition from liquid to gas) requires thermal
energy, which is partly extracted from the water inside the jug,
cooling it down. One 1995 study showed that, under optimal
conditions, a cooling of up to 15 degrees Celsius can be obtained.
Glazed botijos often sold as tourist souvenirs do not cool water as
it cannot evaporate through the glaze.
The botijo is a mobile refrigeration device, for which there exists
no modern counterpart. Plastic, glass or metal bottles, which have
no pores are unable to 'sweat'.