Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn

SODIS frequently asked questions

1. Can you use glass bottles for SODIS?
 
Yes. The only requirement for the bottles is that they are transparent (translucent is not sufficient). People tend to use plastic bottles more than glass for SODIS but that is because they are usually more easily obtained, less fragile and have no monetary deposit associated with them.
 
2. What volume container/bottle is suitable for SODIS? 
 
We have obtained successful and complete inactivations using plastic bottles that range in size from 0.3L up to 19L. 
 
3. Can you use SODIS if the water is cloudy (turbid)?
 
Yes. SODIS will improve the quality of the water regardless of the degree of turbidity. The most effective and quickest removal of microbial pathogens will be obtained with clear water. Some practitioners say that if you place the bottle onto newspaper and cannot read the text through the water then it is not suitable but the very first health impact study of SODIS among the Maasai was with extremely turbid water and even then significant reductions in incidences of childhood diarrhoea were observed.  
 
4. How long should the water be stored before use, after SODIS has been carried out?
 
We recommend that solar disinfected water be consumed within 48 hours of completion of SODIS.
 
5. Why should we consume solar disinfected water within 48 hours?
 
Full disinfection corresponds to (internationally accepted standards of) reductions in bacterial levels from more than 1 million to 0 colony forming units/100ml. Although scientifically unlikely, there is a mathematical possibility that some bacteria might be present at concentrations less than the limit of detection. As a safety precaution we recommend that the water be consumed within 48 hours and if not then it should be solar disinfected again.
 
6. Do we have to drink solar disinfected water immediately after exposure?
 
The water is safe to drink after 6 hours however few people enjoy drinking warm water. Consequently most SODIS practitioners allow the water to cool overnight before consuming it. In practice there are usually two bottles in use. While one bottle is being solar disinfected today, they drink from the bottle which was treated on the previous day.
 
7. Is there any risk of chemicals from the plastic containers making their way into the water after prolonged use of SODIS?
 
This concern is frequently voiced. Several long term studies have been conducted into identifying if there are any risks posed from deterioration of the plastic (see M. Wegelin, et al.  J. Water SRT – Aqua 50 (2001) 125–135..and E. UbombaJaswa et al.  J. Hazard Mater. 8 (2010) 712–719). So far, no hazardous chemicals have been identified. Nevertheless for the sake of completeness we recommend that you replace plastic bottles every six months).