Lime-sun mixer makes drinking water safe

A dash of lime juice and a dose of sunshine make a cheap, effective combination for safer drinking water in impoverished countries. Adding lime juice to water being treated with a solar disinfection method removes detectable levels of harmful bacteria such as E. coli significantly faster than solar disinfection alone, researchers say. “For many countries, access to clean drinking water is still a major concern,” says Kellogg Schwab, professor of environmental health science at Johns Hopkins University and director of the Global Water Program. “Previous studies estimate that, globally, half of all hospital beds are occupied by people suffering from a water-related illness.” Schwab, senior author of a study published in the April issue of the American Journal of Tropical Medicine and Hygiene, says the research showed that solar disinfection of water combined with the citrus juice greatly reduces E. coli levels in just 30 minutes—on par with boiling and other household water treatment methods. In low-income regions, solar disinfection is used in the home to reduce diarrheal illness. One method recommended by the U.N. Children’s Fund is known as SODIS, or solar water disinfection. It calls for filling 1- or 2-liter PET plastic bottles with water and then exposing them to sunlight for at least six hours. In cloudy weather, exposure times of up to 48 hours may be necessary. The 30 milliliters of Persian lime juice per 2 liters of water used in the study to speed up the process—roughly an ounce per half gallon—would “likely not be prohibitively expensive or create an unpleasant flavor,” Schwab says. Schwab and Alexander Harding, lead author and a medical student at the Johns Hopkins School of Medicine, designed their study to determine if lime constituents known as psoralenes could enhance solar disinfection of water. The researchers filled PET plastic bottles with dechlorinated tap water and then added lime juice, lime slurry or synthetic psoralen, and either E. coli, MS2 bacteriophage or murine norovirus. Levels of both E. coli and MS2 bacteriophage were significantly lower following solar disinfection when either lime juice or lime slurry was added to the water. Noroviruses, however, were not dramatically reduced using the technique, indicating it is not a perfect solution. “Many cultures already practice treatment with citrus juice, perhaps indicating that this treatment method will be more appealing to potential SODIS users than other additives such as TiO2 [titanium dioxide] or H2O2[hydrogen peroxide],” the authors write. They caution, however, that “additional research should be done to evaluate the use of lemon or other acidic fruits, as Persian limes may be difficult to obtain in certain regions.” The research was supported in part by the Osprey Foundation of Maryland, the Johns Hopkins University Global Water Program, and the Johns Hopkins University School of Medicine.