Solar Disinfection (SODIS)
Disinfecting water by filling clear bottles and exposing them to sunlight for hours.
SDG 6 Clean Water & SanitationWhat is it?
SODIS fills clear PET bottles with low-turbidity water and leaves them in direct sun for about six hours (or two days if cloudy). UV-A and heat inactivate pathogens.
Why does it matter?
It needs almost no cost or equipment beyond bottles and sunlight, making it accessible to the poorest households.
How does it work?
Solar UV-A radiation damages microbial DNA and, combined with mild heating, inactivates bacteria, viruses, and some protozoa in clear water.
Who benefits?
Very-low-income households in sunny climates, and emergency settings where no other treatment is available.
Who may be disadvantaged?
Households in cloudy or high-latitude regions, or with turbid water, get unreliable results; the small daily volume limits large families.
What evidence exists?
Trials show reductions in diarrhoeal disease, but effect sizes vary and adherence is often low because the method is slow and volume-limited.
What tradeoffs exist?
Free and simple, but slow, weather-dependent, low-volume, and reliant on clear water and intact bottles.
Common misconceptions
Coloured or scratched bottles and turbid water sharply reduce effectiveness; SODIS is not a guaranteed disinfectant under all conditions.
What you can do next
Weigh SODIS against boiling and chlorination for your climate and water clarity, and review the Cochrane review on how sustained use affects real-world impact.