Solar Water Disinfection
Solar Water Disinfection is using sunlight to kill germs in water by placing it in clear bottles.
Sunlight cleans water much like a hot oven cleans raw food. You place a clear bottle of water flat in direct sun. The sun rays pass through the bottle and heat the water inside. That heat kills germs, just as oven heat kills germs in raw dough.
Explaining solar water disinfection by grade level
Germs can hide in water and make you sick. But sunlight can kill those germs. You fill a clear bottle with water and leave it in the sun. After a few hours, the sun's rays make the water safe to drink.
Projects that explore solar water disinfection
Sunlight passes through a clear container and kills germs inside the water — but only if the surface lets it through. When a bottle's outer surface is scratched to different levels of opacity, less UV reaches the bacteria inside. This experiment makes that effect measurable: four PET bottles are scratched to 25%, 50%, 75%, and 100% opacity, then filled with tap water mixed with E. coli culture and left in direct sunlight for six hours. The clear unscratched bottle shows zero bacteria. More scratches mean more bacteria survive.
Ultraviolet rays from the sun can damage bacteria cells — but does that effect work on real water sources? This project tests exactly that. You collect water from three sources: a tap, a drain, and a lake. Before and after leaving each transparent bottle in sunlight for two days, you swab samples onto agar dishes and let colonies grow for five days. The results show how much smaller the colonies are in sun-exposed water compared to the originals, revealing how much the sunlight reduced bacteria growth.