In low-income countries, one way to make drinking water safer is to expose it to sunlight, but now scientists at the Johns Hopkins Bloomberg School of Public Health and the Johns Hopkins School of Medicine, suggest adding lime juice can make the method more effective.

They write about their findings in the April 2012 issue of American Journal of Tropical Medicine and Hygiene.

Senior author Dr Kellogg Schwab is director of the Johns Hopkins University Global Water Program and a professor with the Bloomberg School’s Department of Environmental Health Sciences.

Schwab, a microbiologist in search of ways to detect and eliminate water-borne pathogens, told the media:

“For many countries, access to clean drinking water is still a major concern. Previous studies estimate that globally, half of all hospital beds are occupied by people suffering from a water-related illness.”

Schwab and colleagues found when they added lime juice to water undergoing solar disinfection, it singificantly speeded up removal of detectable levels of harmful bacteria such as Escherichia coli (E. coli).

In fact, they found adding the lime juice meant E. coli levels reduced in just 30 minutes, bringing the treatment on a “par with boiling and other household water treatment methods,” said Schwab.

“In addition, the 30 milliliters of juice per 2 liters of water amounts to about one-half Persian lime per bottle, a quantity that will likely not be prohibitively expensive or create an unpleasant flavor,” he added.

In low-income countries, one of several ways of making water safe to drink and reduce diarrheal illness is solar disinfection, such SODIS (Solar water Disinfection), the method recommended by the United Nations Children’s Fund (UNICEF).

In the SODIS method you fill a one or two-litre polyethylene terephthalate (PET plastic) bottle with water and then expose it to sunlight for at least 6 hours, or up to 48 hours on cloudy days.

For the study, Schwab and colleagues investigated whether psoralens, one of the active constituents in limes, could enhance solar disinfection of water.

They filled PET bottles with dechlorinated tap water and then added lime juice, lime slurry, or synthetic psoralen and either E. coli, MS2 bacteriophage or murine norovirus.

They looked at microbial reductions after exposure to both sunlight and simulated sunlight.

The results showed that compared to solar disinfection alone, levels of E. coli and MS2 bacteriophage were significantly lower when solar disinfection was accompanied by the addition of either either lime juice or lime slurry to the water.

However, lime juice is not a perfect solution, because it had little impact on the noroviruses.

The authors write:

“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].”

However, they call for further studies to find out whether lemons or other acidic fruits will also do the job, as Persian limes are not easy to obtain in some countries.

Funds from the Osprey Foundation of Maryland, The Johns Hopkins University Global Water Program, the Johns Hopkins University School of Medicine Dean’s Funding for Summer Research and the Johns Hopkins University School of Medicine Scholarly Concentrations helped pay for the study.

Written by Catharine Paddock PhD