SODIS Method Makes Water Safe to Drink

Reading time: 4 – 6 minutes

Each year, nearly one billion people around the world lack access to safe, clean water [1]. Water is essential for life, yet less than 1% of water on the planet is safe to drink. This is especially a problem in developing countries or during natural disasters. Take Hurricane Katrina: back in 2005 when it hit the Gulf Coast, one of the biggest needs for storm victims was access to clean drinking water.

In the United States and Europe, people take it for granted that when they turn on the faucet, clean water will flow out. Indeed, a single flush of a toilet in the West uses more water than most Africans have to perform an entire day’s washing, cleaning, cooking and drinking [2].

Securing access to safe water worldwide is vitally important. Clean water is essential for agriculture, food and energy production, recreation and reduction of poverty. More than 2 million people, most of them children, die every year from water-borne diseases. And time is of the essence: by 2020, more people could die of water-related diseases than those that have died due to HIV/AIDS [2].

SODIS in Indonesia

In the 1990s, researchers figured out a simple, free and effective way to clean polluted water and kill disease-causing organisms, including E. coli, Vibrio cholera (which causes cholera, an infection of the small intestine), Salmonella (which causes typhus) and Yersinia enterocolitica (which causes diarrhea) [3]. Solar water disinfection, known as SODIS, is a method of disinfecting water using only sunlight and transparent polyethylene terephthalate (PET) plastic bottles (think: clear 2-liter soda bottles).

The first study to evaluate the effect of the SODIS method on health was investigated by the Royal College of Surgeons of Ireland. Carried out in Kenya, research showed that 16-24% of diarrhea-type illnesses and 86% of cholera occurrences were avoided [4]. Since then, many scientific studies have confirmed the effectiveness and reliability of the SODIS method.

The SODIS procedure is incredibly simple: contaminated water is filled in a transparent PET-bottle and exposed to the sun for 6 hours (or 2 days under very cloudy conditions). During exposure, ultraviolet (UV) radiation from the sun kills disease-causing pathogens. Moreover, infrared radiation heats the water. The combined exposure to UV plus heat in the SODIS process has a synergistic effect on microbial inactivation.

However, scientists don’t yet understand how UV kills germs. Researchers currently think that the bacteria die because cellular respiration — the process in which nutrients are converted into useful energy in a cell — is damaged by UVA radiation so severely that it can’t be repaired.

SODIS method

The SODIS method together with washing hands particularly effective at preventing diarrheal diseases. A systematic study found that while better better sanitation facilities prevented 32% of diarrhea cases, treatment of drinking water in the home (e.g. SODIS method) prevented 39% of diarrhea cases [5]. Incredibly, hand washing was the most effective, preventing almost half (45%) of all diarrhea cases.

The SODIS method is used around the world in places like India, Cameroon, Bolivia, Kenya, Nepal and Nicaragua. So why then are people in developing countries going without clean water? According to a 2008 report by Urs Heierli of msd consulting GmbH, a Swiss company focused on market-based development interventions, it’s difficult to persuade the poor to use SODIS and to ensure that those who have been persuaded continue to use it [6].

The World Health Organization (WHO), UNICEF, and the American Red Cross all recommend the SODIS method as a way to treat drinking water in developing countries. Indeed, it is an ideal way solve one of the world’s most vital issues: making clean water.


  1. Water Facts. Accessed 2011 Jul 8.
  2. Dying for A Drink of Clean Water. The Washington Post. 2005 Sep 20.
  3. SODIS: Microbiology. Accessed 2011 July 8.
  4. SODIS: Health. Accessed 2011 July 8.
  5. Fewtrell et al. Water, sanitation, and hygiene interventions to reduce diarrhoea in less developed countries: a systematic review and meta-analysis. Lancet Infect Dis. 2005 Jan;5(1):42-52.
    View abstract
  6. Heierli, U. Marketing safe water systems: why it is so hard to get safe water to the poor – and so profitable to sell it to the rich. Bern, Switzerland, Swiss Agency for Development and Cooperation (SDC). 2008.
About the Author

Walter Jessen, Ph.D. is a Data Scientist, Digital Biologist, and Knowledge Engineer. His primary focus is to build and support expert systems, including AI (artificial intelligence) and user-generated platforms, and to identify and develop methods to capture, organize, integrate, and make accessible company knowledge. His research interests include disease biology modeling and biomarker identification. He is also a Principal at Highlight Health Media, which publishes Highlight HEALTH, and lead writer at Highlight HEALTH.