Nothing mentioned, nothing gained

SODIS: How the sun could save your life

The quiet, leafy suburb of Dublin in which I currently live has traditionally been a bastion of privelage, with a lot of more old Dublin money and a lot less of the desperation that abounds in other parts of the city. The good people of Clontarf expect life to be effortlessly idyllic.

When a routine test showed that our drinking water was contaminated with an unknown bacterium and unsafe for drinking, the locals were most annoyed. For me, it was a sharp reminder of what we in the developed world take for granted. We wash our clothes, our food, and ourselves in it. We drink it and cook with it to sustain our lives, and then we brush our teeth with it. It comes at the turn of a tap, and the idea that it is anything but good for us is alien. The idea that a glass of water could kill us is simply absurd.

Drinking Water

Drinking Water (Photo credit: SEDACMaps)

But that is the reality for much of the world. In the developing world, four-fifths of all illness is caused by drinking unclean water. Diarrhoea is unpleasant for anyone, but with access to medical care, is unlikely to be fatal. In Africa, it is almost certain to be fatal, especially in children – diarrhoea is the leading cause of childhood death in developing countries and accounts for 4% of all deaths worldwide (WHO). And then there are any number of worms and parasites, and deadly diseases such as salmonella, cholera, and leptospirosis. Much of the developing world’s health burden rests on harrowing diseases which are easily treatable with modern medicines readily available in the developed world, and which could be prevented by simply providing clean, safe water.

This may sound easy and straightforward. But consider the cost and infrastructural demands of

English: Illustration of a typical drinking wa...

English: Illustration of a typical drinking water treatment process. (Photo credit: Wikipedia) Treatment plants like this are unrealistic in many parts of the world.

putting in a sophisticated, complicated water treatment plant in areas of the world where water is still drawn from wells and rivers? Couple this with a lack of people with the expertise to run such plants, inhospitable terrains, local corruption and the lack of political will to affect change from the West, and suddenly a straightforward solution doesn’t seem quite as realistic.

If only there was a simple way to make drinking water safer. A method requiring very little training and very few resources, that anyone could do by themselves, even if they only had a little water to start with. A method that could be used anywhere, anytime – and one which wouldn’t use enormous amounts of energy or produce any waste to damage the environment. Well, now, thanks to science, there is.

The SODIS method is an elegantly simple and surprisingly effective way to make drinking water safe. Contaminated or suspect water is placed in clear plastic or glass bottles and exposed to sunlight for at least six hours. During that time, the UV light emitted by the sun attacks bacterial DNA, killing off dangerous species such as the ones that cause diarrhoea, saving millions of lives across the world. DNA is like the secret code to life – every cell in our body is created through a pathway that begins with DNA. DNA is called into its own every time we need a new cell, so that every time a cell dies due to age or injury, we rely on DNA to fix us. Bacteria are no different. Without properly functioning DNA, life can not exist. Cancer is the chief example of how devastating the consequences can be when DNA goes wrong.

SODIS water disinfection in Indonesia

SODIS water disinfection in Indonesia (Photo credit: Wikipedia)

UV light is already known for its ability to deform DNA, the fundamental unit of life. This mutagenic ability – the ability to change DNA is something we both benefit and suffer from. The damaging effects of over-exposure to UV radiation are the basis for warnings about sunbeds and sunsmart slip-slap-slop type public health campaigns all over the world. Yet research labs such as the one I work in use high-powered UV lighting to sterilise our working areas and keep our experiments contamination free. Some food is treated with UV light to keep it safe and sterile.

But why do we think that simple sunlight is enough to destroy dangerous bacteria in just a few hours when we expect humans to go about and live their lives as normal? Partly, the answer is that in countries where SOLDI is likely to be of most use – the hot, bright deserts of sub-Saharan Africa – the people have adapted biologically and culturally to withstand the sun’s intensity. But bacteria are much, much more susceptible to having their DNA damaged than humans and other animals are. DNA looks like a rope ladder, with two long, ribbon-like strands intertwined around each other. The ribbons are joined by chemical bonds which make up the rungs of the ladder. It’s critically important that these chemical bonds start and end at the right place, and that the right DNA component (DNA is made up of nucleotides or nucleic acids) is matched with the correct partner. By breaking these bonds and mixing them up, UV light distorts the famed double-helix and renders DNA at best non-functional and at worst harmful to its owner.

Animation of the structure of a section of DNA...

Animation of the structure of a section of DNA. The bases lie horizontally between the two spiraling strands. (Photo credit: Wikipedia)

Human DNA is well-protected, deep within the cell, where it is harder for UV light to penetrate. The thin cell walls of bacteria, on the other hand, do little to shield their DNA, especially when exposed to a high level of direct sunlight. As bacterial species consist of one single cell, there is very little “redundancy” or backup DNA if something goes wrong, and furthermore, bacteria and viruses have not developed ways to repair their DNA if something goes wrong in the way that humans have.

SOLDI’s genius is its simplicity. It uses something that is readily available in many of the world’s poorest countries, especially in countries so arid that people can’t be choosy about the water they drink. It doesn’t need a high level of expertise, and the only external resource it needs are a few glass or plastic bottles. High-level scientific research has been done to show that SOLDI is effective. In Sikkim, India, just four weeks of using SOLDI to decontaminate drinking water reduced childhood diarrhoea by 75.88%. A study carried out here, at the Royal College of Surgeons in Ireland, found that SOLDI kills a range of harmful bacteria, including Salmonella and E coli species.

This poster, in Spanish, is shown in schools in South America to educate children about the SODIS method.

SODIS is not a panacea for all the world’s ills, whether water-borne or not. As a scientist raised and educated in the western world, I tend to take it for granted that people understand the microbial basis of many infectious diseases, and appreciate that sterilising food and water to destroy harmful bacteria will prevent disease and promote better health. But that may well not be understood in many parts of the world and there have been issues with people failing to leave the water for long enough for it to be disinfected fully. There are some species of bacteria which can form protective shells, known as spores, to survive stressful conditions. And there is always the potential for corruption if the scheme is to be rolled out large-scale worldwide. But although nothing is without its potential problems, SODIS has made an overwhelmingly positive impact on global health. Eawig, the leading Swiss aquatic research centre who first developed SODIS and whom are working to improve and disseminate solar disinfection methods, estimate that 5 million people use SODIS to clean their drinking water – as Philippe Cousteau, renowned Ambassador for the Environment and a special Correspondent for CNN International, noted “SODIS is a wonderful gift to the world.”

English: SODIS projects in 2010 Français : Pro...

English: SODIS projects in 2010 Français : Projets SODIS en 2010 (Photo credit: Wikipedia)


Solar disinfection improves drinking water quality to prevent diarrhea in under-five children in sikkim, India. Rai BPal RKar STsering DCJ Glob Infect Dis. 2010 Sep;2(3):221-5.

Bactericidal effect of solar water disinfection under real sunlight conditions. Boyle MSichel CFernández-Ibáñez PArias-Quiroz GBIriarte-Puña MMercado AUbomba-Jaswa EMcGuigan KGAppl Environ Microbiol. 2008 May;74(10):2997-3001.



One comment on “SODIS: How the sun could save your life

  1. Pingback: Purify Water in 6hrs without Chemicals or Filters « Alex Czartoryski's Blog

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