Solar Water Disinfection put to test

August 19, 2009

A recent study [1] of Solar Water Disinfection (SODIS) has attracted substantial media attention for its negative findings on the SODIS process, in which water is disinfected by placing it in PET bottles and exposing it to sunlight. The investigators reported that the incidence of diarrheal diseases was not significantly decreased in an intervention group as compared with a control group. The authors of the study suggest to "hold off" on new promotion campaigns for the method. This would be wrong.

The intervention group included both SODIS users and non-users and the reported rate of SODIS use was only 30% - the actual consumption of SODIS-treated water in the household may have been as low as 14%. The report concluded that further research including “a direct comparison of SODIS to alternate drinking water treatment methods [is] needed before further global promotion of SODIS.”

As researchers of the SODIS process and advocates of its use, we must challenge this conclusion. An estimated 3 million people in 30 countries are currently using SODIS to reduce their risk of water-borne disease. Numerous studies have reported health benefits of SODIS when it is correctly and consistently used. In one such study, the incidence of cholera during an epidemic in Kenya was 88% lower among SODIS than non-users. [2]

A well-known weakness of the SODIS process is that it is often not used consistently or is used to treat only a fraction of the drinking water consumed. Beneficial health impacts associated with the use of SODIS may also be compromised by poor sanitation and hygiene. Nonetheless, we feel that people should not be discouraged from continuing to use SODIS or from adopting it unless an alternate supply of safe drinking water is available.

We strongly support continued studies of the effectiveness of SODIS and other methods to reduce the incidence of water-borne disease. We suggest, however, that recommendations based on such studies be tempered by the recognition that people who are using (or might adopt) SODIS have no alternative source of safe drinking water. In contrast to the recommendation of Mäusezahl and co-workers, we suggest that future education of SODIS users should focus on establishing the regular practice of the method and also on eliminating the consumption of any untreated and contaminated water.

[1] Mäusezahl et al. (2009). Solar Drinking Water Disinfection (SODIS) to Reduce Childhood Diarrhoea in Rural Bolivia: A Cluster-Randomized, Controlled Trial. PLoS Med 6(8)

[2] Conroy et al. (2001). Solar disinfection of drinking water protects against cholera in children under 6 years of age. Arch Dis Child. Oct; 85(4):293-5.

• More information can be found here [pdf].
  
• The new study is published in the newest edition of PLoS Medicine.