The Best Disinfectant

People have known of the effectiveness of sunlight in helping people recover from illness, and early work on bacteria showed that sunlight could indeed kill micro-organisms. The efficacy of sunlight as a germicidal agent was worked into sanitation designs from the turn of the century. Then it was learned that ultraviolet light with wavelengths shorter than those transmitted by the atmosphere were even more effective at killing germs. Recently SODIS—SOlar DISinfection of contaminated water, a very simple process that uses only ordinary sunlight and no shortwave rays—provides a surprisingly effective, low-tech method for killing harmful microorganisms in water. How can this possibly work?