Context: Solar water disinfection (SODIS) involves exposing water-filled plastic polyethylene terephthalate (PET) bottles to sunlight for several hours. Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions. It is recommended by the World Health Organization as a viable method for household water treatment and safe storage. Over two million people in developing countries use this method for their daily drinking water.

Question: Solar water disinfection is recommended by which organization?
Answer: the World Health Organization

Question: How long should the plastic bottles filled with water be exposed to sunlight during Solar water disinfection?
Answer: a minimum of six hours to two days during fully overcast conditions

Question: What does the World Health Organization say about Solar water disinfection?
Answer: a viable method for household water treatment and safe storage

Question: How many people use Solar water disinfection to disinfect their drinking water?
Answer: Over two million people in developing countries