Water is essential for life. Yet the quality of water available to most of the developing world continues to worsen. According to the World Health Organisation (WHO), “at any given time perhaps one-half of all people in the developing world are suffering from one or more of the six main diseases associated with water supply and sanitation (diarrhoea, ascaris, dracunculiasis, hookworm, schistosomiasis, trachoma)”. The number of people dying from diarrhoeal diseases is equivalent to twenty fully loaded jumbo jets crashing every day, leaving no survivors. In Brazil, this problem is being remedied through water treatment in the home. Solar disinfection (SODIS) provides a simple, low-cost, environmentally sustainable and easily replicable treatment for contaminated water.
Water Borne Disease
The six main diseases associated with water supply and sanitation
- Ascaris is a worm that lives in the small intestine. Infection with Ascaris is called ascariasis.
- Dracunculiasis, more commonly known as Guinea worm disease, is a preventable infection caused by the parasite Dracunculus medinensis.
- Hookworm is an intestinal parasite of humans. One of the most common species, Ancylostoma duodenale, is found in southern Europe, northern Africa, northern Asia, and parts of South America.
- Schistosomiasis, also known as bilharzia, is a disease caused by parasitic worms. Infection with Schistosoma mansoni, S. haematobium, and S. japonicum causes illness in humans.
- Trachoma is an easily spread infection of the eye. Repeated occurrences scar the upper eyelid, eventually turning it inward. The eyelashes then scratch the cornea, leading to blindness.
Those at greatest risk of contracting water-borne diseases are children, people living in unsanitary conditions, and the elderly. Frequent attacks of diarrhoeal diseases can cause these groups to become malnourished and more susceptible to other diseases.
“Despite decades of effort…and $30 billion of water investment in developing countries each year…an estimated 10,000 people…die everyday from water and excreta- related diseases. Thousands more suffer debilitating illnesses. The tragedy is that these deaths and illnesses are entirely preventable.” (World Bank)
The greatest microbial risks are associated with ingestion of water that is contaminated with human or animal faeces. Faeces can be a source of bacteria and viruses that cause life-threatening diseases such as cholera and diarrhoea. Water quality varies rapidly over a wide range, with short-term peaks in bacteria concentration increasing disease risks and triggering outbreaks of water-borne disease.
One solution would be to provide systems of piped, disinfected water to everyone. However, this is expensive, time-consuming and often beyond the immediate capabilities of developing countries. To address immediate needs, other approaches are required while progress is made in improving infrastructure. For this purpose, a number of technologies, including physical and chemical treatment methods, are used to improve the microbial quality of household water and to reduce water-borne disease.
Physical methods include boiling or heating (using fuel and solar energy), settling, filtering, exposing to the UV radiation in sunlight, and UV disinfection with lamps. The chemical methods include coagulation-flocculation and precipitation, adsorption, ion exchange and chemical disinfection with germicidal agents (primarily chlorine). Some water treatment and storage systems use chemicals and other materials that cannot be easily obtained locally at a reasonable cost. They may also require relatively complex and expensive systems and procedures to treat the water. Such systems may be too inaccessible, complex and expensive for treatment and storage of water in some places and settings. They also have their limitations for purifying water:
- Storing water is the simplest method of improving its quality. While this will clear sedimentation, it will only be partially effective in removing turbidity (muddiness) and faecal contamination.
- Boiling water is the best method of ensuring sterile, pathogen-free water of high quality. However, boiling water takes up a lot of energy (solar power and fuel) – so not everyone can afford it.
- Pasteurisation is achieved by heating water to 70-75°C, and maintaining the heat for 10 minutes. This also requires high energy input.
- Filtration will remove much of the solid matter and sediment, but is largely ineffective against micro-organisms. Filtration devices are also costly to buy and install.
- Chlorine will kill micro-organisms such as bacteria and viruses, but is unable to fight pathogenic parasites such as Giardia, Cryptosporidium and Helminth eggs. It also requires skilled application, since chlorine is a corrosive substance. Treated water has a distinct taste which is not to everyone’s liking.
Household water treatment and safe storage (HWTS) interventions can lead to dramatic improvements in drinking water quality and reductions in diarrhoeal disease, making an immediate difference to the lives of those who rely on water from polluted rivers, lakes and, in some cases, unsafe wells or piped water supplies. The extent to which improved household water quality reduces diarrhoeal disease depends on a variety of technology-related factors as well as site-specific environmental and demographic factors. Reductions in household diarrhoeal diseases of 6-90 per cent have been observed, depending on the technology and the exposed population and local conditions. In Brazil, a campaign has been launched to encourage the use of a solar disinfection process known as SODIS, which has a documented efficiency of over 99.9 per cent in 81.2 per cent of samples.
Solar disinfection, or SODIS, provides a low-cost, easily applicable means of ensuring clean, drinkable water. The technique of solar disinfection uses the sun’s radiation (specifically ultra-violet-A (UV-A) rays and heat) to destroy pathogenic micro-organisms present in the water. Its efficiency in killing disease-carrying bacteria depends on the water reaching a certain heat through exposure to sunlight. To achieve this, transparent plastic containers are filled with water and exposed to full sunlight for at least six hours.
The solar disinfection approach to treating contaminated water was first presented by Professor Aftim Acra in a booklet published by UNICEF in 1984. Following this, a research team from EAWAG (Swiss Federal Institute of Environmental Science and Technology) and SANDEC (Department of Water and Sanitation in Developing Countries) embarked on laboratory research on the effectiveness of solar radiation as a means of disinfecting water. These tests revealed that the combined use of UV-A radiation and increased water temperature through exposure to sunlight can improve the microbiological quality of drinking water. Subsequent field tests and pilot demonstrations have proved the viability of the system, its socio-cultural acceptance and affordability. Pilot demonstrations were done in many developing countries which enjoy good sunlight throughout the day – Colombia, Bolivia, Burkina, Togo, Thailand and Indonesia.
How it works
SODIS is a simple and easily replicable method of providing enough clean drinking water for the household. For the method to work well, the exposure to sunlight should be at least six hours, or until the water reaches a temperature of 55°C.
- Clear plastic bottles are used for SODIS application. These bottles should be filled with relatively clear water, since SODIS is not effective when the water turbidity is high. Water turbidity should not be more than 30 NTU (Nephelometric Turbidity Units). The bottles should be transparent and clear, not coloured or discoloured, and not old or damaged. Plastic bottles are preferred since they let in more UV radiation than glass bottles, and are unbreakable, cheap and easily replaceable.
- The water in these bottles should be exposed to full sunlight for six hours, or for two consecutive days during cloudy skies to ensure maximum benefit of the solar effect on pathogens. The water is ready for consumption immediately after adequate sunlight exposure. The water must be handled with clean hands so that there is no secondary contamination of disinfected water.
The role of oxygen
Sunlight has a direct impact on micro-organisms, as UV-A radiation is directly absorbed by organic material. Sunlight radiation also produces highly reactive forms of oxygen, which kill the micro-organisms. Reactive forms of oxygen include oxygen free radicals and hydrogen peroxides. These are a temporary product of the action of sunlight on microbes in oxygenated water. There is no significant enduring effect once the sample is removed from the sunlight. This process is known as ‘solar photo-oxidative disinfection’. The microbes exposed to reactive oxygen are oxidised during treatment.
On a practical level, aeration can be achieved by stirring the untreated water vigorously before filling the SODIS containers or by shaking half-filled containers thoroughly and then filling them completely before sunlight exposure. In particular, stagnant water drawn from ponds, cisterns and possibly wells should be aerated to enhance the inactivation of micro-organisms by SODIS. Other ways to improve the efficiency of SODIS include:
- Put black paint on half of the outer surface of the bottle and lay the bottle blackened-side downwards. This increases the rate of heating.
- Place the bottles on a reflective surface, such as aluminium foil, as this can dramatically increase the rate of water heating.
- Place bottles horizontally and not upright.
- Ensure the bottles are full.
- Always replace scratched and old bottles.
- Check that the climate and weather conditions are suited for SODIS –there should be bright weather with no more than 50 per cent cloud cover.
- Collect plastic bottles of 1 litre or 1½ litre volume. PolyEthylene Terephthalate (PET) bottles are preferred to PVC, because PVC can contain harmful additives, and to glass, because glass blocks out some of the UV rays.
- A family should have four plastic bottles, two for the day’s consumption and two exposed to the sun.
- Check that the screw cap is watertight and clean.
- Bottles should be laid out on a suitable heat-reflecting surface, such as roofing sheets or corrugated iron, in a clear spot on the roof or in the garden. The bottles should be exposed to direct sunlight for at least six hours.
- If the water has a lot of discoloration and sediment, the water has to be pre-treated (e.g. chemically) before SODIS application.
- It is best to have a specific person responsible for exposing the SODIS bottles to the sun. At least two members of each family or community must be trained in the correct application of SODIS, especially on the importance of maintaining sun exposure throughout the period.
People’s health will not improve just because they have new equipment or facilities – they have to use them. Minor improvements to existing water supply practices are more likely to be accepted than major and sudden changes. SODIS will only be used and applied if the target population is convinced of its advantages over the traditional ways of treating and handling drinking water. Consumers need to be fully aware of the bacteriological transmission routes of water-borne diseases and how to reduce or avoid them. Finally, private users will only invest in water treatment if they believe they will benefit directly – as health benefits are often indirect, they may be perceived only in the long-term.
According to SODIS field experiments conducted by EAWAG and SANDEC, 84 per cent of users continued to use SODIS, 13 per cent considered continued use, and only 3 per cent refused to use SODIS, as they believed that their health was not affected by the existing water quality. Reasons for people accepting SODIS included:
- It is easy and practical;
- It provides good quality, clean drinking water;
- It incurs less of a burden on the daily routine than travelling to get safe drinking water;
- Its use reduces sickness, diarrhoea and stomach-aches;
- It lowers costs;
- It improves quality of life.
However, measuring the health impact of SODIS is very difficult, as the multiple factors of disease transmission have to be considered in the evaluation. Four studies carried out by EAWAG and SANDEC measured the effectiveness of SODIS on the health improvement of children of various ages.
The results from the studies were summarised as follows:
- SODIS reduces the number of new cases of diarrhoea
For children aged 5-16 years, the number ofnew cases of diarrhoea in families using SODIS is 10 per cent less than in familiesthat do not use the method. For children under 5 years there is a reduction of 16 per cent of diarrhoeal illnesses among SODIS users. Childhood diarrhoea is significantly less frequent in villages with a strong committee, high level of village organisation and commitment to community development, which lead to a better adoption of SODIS.
- SODIS reduces the number of severe cases of diarrhoea
There is a 24 per cent reduction in the incidence of severe diarrhoeaamong children of families that use solar disinfection of drinking water.
- SODIS helps to prevent cholera
Among SODIS users, children below the age of 6 are considered eight times less likely to contract cholera. For older children, adolescents and adults no preventive effect was found. This could be attributed to the fact that mothers strictly controlled the type of drinking water consumed by their small children, while older people also drank water from contaminated, non-treated water sources.
What SODIS does not do
- SODIS does not change the chemical properties of the water.
- SODIS requires relatively clear water (low turbidity) to work – it is ineffective against highly turbid water.
- SODIS requires suitable weather conditions – it is not effective where sunlight is weak.
- SODIS is not useful for treating large volumes of water.
Department of Health & Human Services. Safe Water Systems for the Developing World: A Handbook for Implementing Household-Based Water Treatment and Safe Storage Projects. Atlanta, USA: Center for Disease Control and Prevention.
Meierhofer, R. and Wegelin, M. (2002). Solar Water Disinfection: A Guide to the Application of SODIS. Duebendorf: Swiss Federal Institute of Environmental Science and Technology (EAWAG) and Department of Water and Sanitation in Developing Countries (SANDEC).
United Nations. World Water Development Report: Water for People, Water for Life.
Fundacion SODIS www.fundacionsodis.org
Swiss Federal Institute of Environmental Science and Technology (EAWAG) www.eawag.ch
Donor and Supporting Organisations
Department for International Development (DFID) www.dfid.gov.uk
World Bank www.worldbank.org
Centre for Disease Control and Prevention www.cdc.gov/safewater
ITDG Technical Briefs answers.practicalaction.org
Safe Water Systems www.safewatersystems.com
UN World Water Assessment Programme www.unesco.org/new/en/natural-sciences/environment/water/wwap
World Health Organisation www.who.int
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