Light Quiz – Using light to purify water

Light Quiz – Using light to purify water

Quiz

In many African countries, drinking water is still taken from rivers, creeks or wells. The tedious work involved is mostly done by women, many of whom have to carry home their heavy load over many miles. Furthermore, this water is often contaminated with pathogens which can cause severe diarrhea. However, there is a simple and cost-efficient method to disinfect water: sunlight.

Question: How can sunlight be used to make contaminated water drinkable?

a) The water must be filled into a black-coated barrel exposed to direct sunlight for at least 24 hours.
b) The water must be filled into a PET bottle exposed to direct sunlight for at least six hours.
c) The water must be filled into a special glass container exposed to direct sunlight for at least six hours.

Answer b) is correct: The water must be filled into a PET bottle exposed to direct sunlight for at least six hours.

It’s quite simple: Just fill three quarters of an empty PET bottle with contaminated water. Then shake the water to ensure that it mixes with the air in the bottle. Afterwards, expose the bottle to glaring sunlight for at least six hours. During this time, the ultraviolet light forms highly reactive radicals from oxygen in the air. Combined with UV radiation, these radicals are simply ideal to effectively kill off bacteria such as cholera, typhus and diphtheria pathogens.