A new study has found that a popular method of disinfecting water with sunlight, used in more than 30 countries worldwide, may be far less effective in real-world settings than it is in the lab.
An estimated 1.8 million people die every year from diarrheal diseases, mainly by drinking or coming into contact with dirty water.
The majority of those nearly two million people are children under the age of five living in developing countries.
Household solar drinking water disinfection, or SODIS, is a simple, low-cost method that involves filling clear plastic bottles, such as old soda bottles, with water containing diarrhea-causing microbes and exposing them to direct sunlight for several hours.
Ultraviolet radiation from the sun and a temperature increase inside the bottles inactivate pathogens, making it safe to drink.
SODIS is currently promoted worldwide by various public health agencies and organizations.
But, according to a report in National Geographic News, the new study suggests that introducing SODIS into communities did not significantly reduce diarrhea rates in rural villages in Bolivia.
Until additional real-world studies of the effectiveness of SODIS are conducted, agencies should "hold off" on new promotion campaigns for the method, according to study leader Daniel Mausezahl, a senior health advisor at the Swiss Tropical Institute in Basel, Switzerland.
Mausezahl and colleagues found that children in families that used the SODIS method had on average 3.6 episodes of diarrhea per year, compared with 4.3 annual episodes in the control group.
The result is not statistically significant enough to show that the small reduction was due to the SODIS method, the study authors said.
The problem is not SODIS, which undoubtedly works, according to Mausezahl.
"SODIS is effective. If you are in dire straits, you can take a SODIS bottle and put river water in it, expose it to the sun for at least six hours, and you can drink it," he said.
Rather, the issue appears to be compliance - getting people to consistently use the SODIS method.
According to Meierhofer Regula, a scientist at the Swiss Federal Institute of Aquatic Science and Technology, compliance is a problem common to all intervention programs that aim to change human behavior, such as hand washing or condom use.
"Instead of scaling back, SODIS promotion should be ramped up, so that people become more familiar and comfortable with it," he said.