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

SODIS water programme

What is solar water disinfection (SODIS)?

Solar water disinfection (SODIS) has been in existence for more than 30 years. The technique consists of placing water into transparent plastic or glass containers (normally 2L PET beverage bottles) which are then exposed to the sun. Exposure times vary from 6 to 48 hours depending on the intensity of sunlight and sensitivity of the pathogens. Its germicidal effect is based on the combined effect of thermal heating of solar light and UV radiation.

The RCSI SODIS initiative was recently featured on the RTE TV programme The Science Squad

Prof. Kevin McGuigan discusses the social side to his work on solar disinfection at a TedX Dublin.

SODIS in action

Diagram of the SODIS technique 

How it works

Transparent containers are filled with contaminated water and placed in direct sunlight for at least six hours, after which time it is safe to drink. Solar disinfection containers (reactors) can be glass or plastic (usually polyethylene-terephthalate – P.E.T.) – even plastic bags have been used. Plastic bottles are more robust than glass bottles since few glass bottles survive an off-road journey in the back of a 4-wheel drive vehicle or a fall from a roof.

It is recommended that solar disinfected water should be consumed within 48 hours to avoid the possibility of post exposure re-growth. The efficiency of the basic protocol can be enhanced by adding a number of additional steps such as:

Placing filled bottles on reflective surfaces to boost the amount of sunlight absorbed by the reactor (Kehoe et al. 2001, Mani et al. 2006).

Painting the underside of the SODIS reactor black to enhance solar heating.

Shaking a two-thirds filled bottle vigorously for 30 seconds before topping up and sealing, to increase initial levels of dissolved oxygen for solar induced oxidative inactivation.

Filtering the water before filling the reactor.

SODIS in the community

SODIS in the Community

Harvested rainwater being solar disinfected in a primary school in Uganda SODIS in the Community
Harvested rainwater being solar disinfected in a primary school in Uganda

SODIS in the Community 

A health worker in Zimbabwe answers questions from a householder who has recently started using SODIS


Solar disinfection of  turbid water taken from an open dug well in rural Uganda

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).

Helpful references

1. Asiimwe JK, et al. Field Comparison of Solar Water Disinfection (SODIS) Efficacy between Glass and PET Plastic Bottles under Sub-Saharan Weather Conditions. Journal of Water and Health. 2013;11.4:729-737. doi: 10.2166/wh.2013.197.

2. Dangour AD et al. Interventions to improve water quality and supply, sanitation and hygiene practices, and their effects on the nutritional status of children (Review). 2013, Issue 8, p1-100. The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.

3. McGuigan KG et al. Solar Water Disinfection (SODIS): A review from bench-top to roof-top. Journal of Hazardous Materials. 2012;235-236:29-46.

4. du Preez M et al. Solar disinfection of drinking water (SODIS) in the prevention of dysentery in Kenyan children aged under 5 years. Environmental Science & Technology. 2011, 45 (21), pp 9315–9323. PMID:21936492

5. McGuigan KG, et al. A high compliance randomised controlled field trial of solar disinfection (SODIS) of drinking water and its impact on childhood diarrhoea in rural Cambodia. Environmental Science & Technology. 2011;45(18):7862-7867. PMID: 21827166

6. Ubomba-Jaswa E, et al. A preliminary Ames-fluctuation assay assessment of the genotoxicity of drinking water that has been solar disinfected in polyethylene terephthalate (PET) bottles. Journal of Water & Health. 2010;8(4):712-719. PMID: 20705982

7. Boyle M, et al. Bactericidal effect of solar water disinfection under real sunlight conditions. Applied & Environmental Microbiology. 2008;74(10):2997-3001. PMID: 18359829.

8. McGuigan KG et al. Batch solar disinfection (SODIS) inactivates oocysts of Cryptosporidium parvum and cysts of Giardia muris in drinking water. J Applied Microbiology. 2006;101(2):453-463. PubMed I.D. 16882154

9. Lonnen J et al. Solar and photocatalytic disinfection of protozoan, fungal and bacterial microbes in drinking water. Water Research. 2005;39(5):877-883. PubMed I.D. 15743634

10. Conroy RM, et al. Use of solar disinfection protects children under 6 years from cholera. Archive of Disease in Children, 2001:85, 293-295. PubMed I.D. 11567937

11. Wegelin M, et al. Does sunlight change the material and content of PET bottles? Journal of Water Science Research & Technology - Aqua 2001;50,125-135.

12. Kehoe SC, et al. Effect of agitation, turbidity, aluminium foil reflectors and volume on inactivation efficiency of batch-process solar disinfectors. Water Research 2001;35(4):1061-1065. PubMed I.D. 11235872

13. McGuigan KG et al. Solar disinfection of drinking water contained in transparent plastic bottles: characterizing the bacterial inactivation process. Journal of Applied Microbiology 1998;84(6):1138-1148. PubMed I.D. 9717300

14. Conroy RM et al. Solar disinfection of drinking water and incidence of diarrhoea in Maasai children: a controlled field trial. The Lancet 1996;348:1695-97. PubMed I.D. 8973432

15. Joyce TM, et al. Inactivation of faecal bacteria in drinking water by solar heating. Applied Environmental Microbiology 1996;62(2):399-402. PubMed I.D. 8593045