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."
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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