SODIS
Practical Action
Boiling water is the best method of ensuring sterile, disease-causing-pathogen-free
water of high quality, but boiling water takes up a lot of energy; not everyone can
afford it.
Pasteurisation is achieved by heating water to lower-than-boiling point, often 70-
75˚C, but maintaining the heat for 10 minutes or so. This also requires high energy
input.
Filtration will remove much of the solid matter and sediment. It is more difficult to
remove micro-organisms, plus, they are costly to buy and install.
Chlorine will kill micro-organisms like bacteria and viruses but it is not so affective in
fighting pathogenic parasites like Giardia, Cryptosporidium and Helminth eggs.
Further, skilled application is necessary since chlorine is a corrosive substance.
Treated water has a distinct taste - not to everyone’s liking.
SODIS – an alternative method
Moving away from conventional water treatment, SODIS provides a simple, low-cost, easily
applicable means of ensuring clean, drinkable water. SODIS or solar water disinfections uses
the sun’s radiation (specifically UV-A rays and heat) to destroy pathogenic micro organisms
present in water. Its efficiency in killing disease-carrying protozoa depends on the water
reaching a certain heat through exposure to sunlight. UV-A rays also drastically reduce many
forms of bacteria that contaminate water. To achieve this, transparent plastic containers are
filled with water and exposed to full sunlight for at least six hours.
SODIS – a history
This interesting approach to treating contaminated water was first presented by Prof. 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 comprehensive
laboratory research on the effectiveness of solar radiation as means of disinfecting water.
These tests revealed that the combined use of UV-A (ultra violet-A) radiation and increased
water temperature through exposure to sunlight can be 99.9% effective in destroying micro
organisms in raw water.
Subsequent field tests and pilot demonstrations have proved the viability of the system in real
life, 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.
Transmission of waterborne pathogens
Many common pathogens (disease-causing micro organisms) are transmitted through water
and other infectious pathways (droplets, food). Poor hygiene is often the cause of infection.
Water transmits bacteria, viruses and types of protozoa, which can cause diarrhoeal diseases.
These pathogens could also be transmitted though food or insects such as flies. Ignoring
healthy practices like washing hands with soap and water, and after disinfecting and
removing faecal matter safely from the environment can increase the risk of disease spread.
Vibrio choshigella, salmonella and different stains of Escherichia Coli (E-coli) are the most
common pathogenic bacteria found in contaminated water, while Hepatitis A and Enterovirus
are the significant viruses. Although helminths and protozoa do not cause diarrhoea, they
can cause chronic digestive illness, which can result in malnutrition. Giardia spp. and
Cryptosporidium ssp. are commonly transmitted through water and have a cystic (egg) stage
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