Metal works best to conduct the heat to the water containers. A reflector to bounce in additional sunlight. If no thermometer is available, heat until bubbles are rising from the bottom steadily. Natural waxes, such as beeswax , can be used to indicate pasteurization temperature. Solar conditions, weather conditions, latitude and box efficiency are all variables that affect the ability of solar boxes to pasteurize water.
Larger boxes can pasteurize more water, smaller less.
Pasteurization kills germs and disease-carrying organisms in drinking water including bacteria, rotaviruses, enteroviruses, and cysts commonly transmitted in contaminated water. Pasteurized water is not sterilized, however, and therefore should not be used for medical procedures. Pasteurization does not remove chemical contamination such as pesticides or industrial wastes. Solar box cookers, in use throughout the world, are also very effective for cooking food.