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Photo: People stand in line for water
Residents wait in line to buy water jugs outside a warehouse in Villahermosa, Mexico, November 2, 2007, after a flood devastated the area.

A new study shows that a popular method of using plastic bottles to disinfect water with sunlight may not help protect people from water borne disease, due partly to stigma.

Photograph by REUTERS/Tomas Bravo

Ker Than

for National Geographic News

Published August 18, 2009

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, a new study finds.

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.

The new study, which appears online this month in the journal PLoS Medicine, 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, said study leader Daniel Mausezahl, a senior health advisor at the Swiss Tropical Institute in Basel, Switzerland.

Clean Water Solutions

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 authors say.

The problem is not SODIS, which undoubtedly works, Mausezahl said.

"SODIS is effective," he said. "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."

Rather, the issue appears to be compliance—getting people to consistently use the SODIS method. The authors note, for example, that while nearly 80 percent of the households reported diligent SODIS use, field-worker observations suggested that only about a third of them actually did so.

There are several reasons why people might slack on SODIS use, Mausezahl said.

For one, they may be too busy. Mausezahl also said he suspects there is a stigma associated with its use.

"People do not want to put a SODIS bottle that is basically reused wastewater on their roofs. It's a signal to everyone else in the community that you don't have money for proper chlorination or a proper water supply."

Nurturing Habits

Meierhofer Regula, a scientist at the Swiss Federal Institute of Aquatic Science and Technology who was not involved in the study, noted that 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, said Regula, so that people become more familiar and comfortable with it.

Kevin McGuignan, the coordinator of the European Union research project SODISWATER, also thinks global SODIS promotion should not be curbed.

"Further research is urgently required in order to gain a clearer picture of why compliance is so low and how it can be improved," he said.

Study author Mausezahl thinks the current global rollout of SODIS is a prime opportunity to conduct exactly this type of research.

"The moment SODIS goes out of the lab something goes wrong. Either we do not communicate properly about it or were applying it in the wrong setting," he said.

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