Sunlight Is An Effective Disinfectant

The setup is simple: Let sunlight beat down on water in clear plastic or glass bottles to kill pathogens inside. The method, known as solar water disinfection or SODIS, has been around for decades and has received the imprimaturs of international health organizations. But its effectiveness in improving health has been questioned. Now field tests in Kenya provide data to support it (Environ. Sci. Technol., DOI: 10.1021/es2018835).

Refined in the 1990s by researchers at the Swiss Federal Institute of Aquatic Science and Technology, SODIS provides a cheap method to treat water in places that lack water treatment plants. A simple, transparent polyethylene bottle, for example, or a glass soda bottle, set in sunlight for six hours, can free water of pathogens like Escherichia coli. But research in Bolivia and elsewhere has found that waterborne illness persisted when people used SODIS to clean their water (PLoS Medicine, DOI: 10.1371/journal.pmed.1000125).

Now researchers led by Kevin McGuigan of the Royal College of Surgeons in Ireland have shown that children in Kenya’s Rift Valley get sick less often when they drink SODIS-treated water, and grow more. Local health workers enrolled 1,000 children, half of whom were randomly assigned to use SODIS, while the other half continued to use their family’s usual water treatment practices.

During multiple visits to the families over 18 months beginning in 2007, health workers collected water samples and measured children’s heights and weights as indicators of their overall health. They also collected caretakers’ diaries of the children’s sick days.

The researchers found that the children drinking SODIS-treated water experienced dysentery about half as often as children not using SODIS did. What’s more, E. coli levels in water samples treated with SODIS were just 3.5% of those in untreated water. Children drinking SODIS-treated water also were ill for fewer days than were those in the control group. The median height of the children increased by 0.8 cm more in the group using SODIS than in the control group, a statistically significant increase, McGuigan says. The weight measurements, however, were confounded by low equipment accuracy and showed no significant difference between groups.

“We were limited in what we could carry with us,” McGuigan says of the difficulties of field work in rural areas in Kenya. In addition, 130 families could not complete the study because they had to flee violence following the country’s disputed 2007 election.

The research “confirms that SODIS can work,” comments Rob Reed of Central Queensland University, in Rockhampton, Australia, but he cautions that where compliance is low, SODIS may not be as effective. The success or failure of SODIS, he says, depends as much on how people use it as on the technology itself.