Clean drinking water in 6 hours

fernandocoelho — Thu, 29 Sep 2011 14:49:40 GMT

SODIS METHOD

Water can be disinfected and in this way made drinkable using the rays of the sun. "Solar water disinfection" - SODIS for short - thus offers a solution for preventing diarrhoea, one of the most common causes of death among people in developing countries.

Clean drinking water in 6 hours

The SODIS method is ideal for treating water for drinking in developing countries. All it requires is sunlight and PET bottles. How does it work? Clear PET bottles are filled with the water and set out in the sun for 6 hours. The UV-A rays in sunlight kill germs such as viruses, bacteria and parasites (giardia and cryptosporidia). The method also works when air and water temperatures are low.

People can use the SODIS method to treat their drinking water themselves. The method is very simple and its application is safe. It is particularly suitable for treating relatively small quantities of drinking water.

How does it work?

The SODIS method is very easy to apply: A transparent PET bottle is cleaned with soap. Then, the bottle is filled with water and placed in full sunlight for at least 6 hours. The water has then been disinfected and can be drunk.

Important points to consider when applying the SODIS method

	Material, colour and shape of the bottle We recommend using PET bottles in the application of the SODIS method because they are light and do not break. They are also easy to obtain in many regions. However, glass bottles or special bags can also be used. PET bottles are usually labelled as such, but they are not called by the same name in all countries. Factsheet Glass vs. PET (EN, FR, ES) Factsheet Bottle vs. Bag (EN, FR, ES) Factsheet Use of Bags (EN, FR, ES) The bottles must be transparent and colourless. PET bottles often have a bluish tinge. This is not a problem. Heavily scratched bottles must be replaced. Factsheet Ageing of bottles (EN, FR, ES) The bottles must not hold more than 3 litres. Factsheet Depth of water (EN, FR, ES)
	Turbidity If the water is very turbid, the effectiveness of the method is reduced. It is very easy to determine whether the water is sufficiently clear: The filled PET bottle must be placed on top of a newspaper headline. Now one must look at the bottom of the bottle from the neck at the top and through the water. If the letters of the headline are readable, the water can be used. If the letters are not readable, the water must be filtered. This test corresponds to a turbidity of 30 NTU. Factsheet Turbidity (EN, FR, ES)
	Cloudiness Cloudiness affects the strength of solar radiation and thus also the effectiveness of the method. Rule of thumb: If less than half of the sky is clouded over, 6 hours will be enough to completely disinfect the water. If more than half of the sky is covered with clouds, the bottle must be placed in the sun for 2 consecutive days. Factsheet Cloudiness (EN, FR, ES) Rain The method does not work satisfactorily during lengthy periods of rain. On these days, we recommend collecting rainwater.
	Preventing recontamination The treated water should be kept in the bottle and drunk directly from the bottle, or poured into a cup or glass immediately before it is drunk. In this way, it is possible to prevent the treated water from becoming contaminated again.

Research

In order to confirm the effectiveness of the SODIS method, it was necessary to carry out microbiological tests. These tests showed that the method reliably kills germs that cause diarrhoea. Besides research in the field of microbiology, several health studies examined the effect of the SODIS method on the spread of diarrhoeal diseases among people who use SODIS. These studies confirm the positive effect of the method for the population. Sociopsychological studies tested different training strategies to find the most effective for educating people in developing countries. These provided us with important information about the best way to implement projects in the field. Analyses of the chemical substances in PET bottles and in the water prove that use of PET bottles does not represent a danger to health.

Microbiology

When developing the SODIS method, it was important to know which germs die and how much sunlight is required to kill them. These questions have been answered for most of the germs that threaten the health of humans. The SODIS method kills bacteria, viruses, and most parasites. We know not only that the germs die; we are also beginning to find out why. more>>

Health

The aim of the SODIS method is to improve the health of the people living in developing countries. To determine whether this was happening, specific studies were necessary. Many tests confirmed the positive effect of the SODIS method; the occurrence of diarrhoea is much less frequent among people who treat their water using the SODIS method than among their neighbours who drink untreated water. The method is responsible for more than a direct improvement in the quality of life of the people concerned. Children attend school more often and their parents can go to work more regularly. more>>

Training strategies

In order for the method to be used all over the world, information about it must be spread as efficiently and inexpensively as possible. For this reason, sociopsychologists have researched a number of different training strategies. Visits to the homes of the people concerned proved to be particularly successful. In these instances, it is essential not only to convince the people to try the method. It is most important to assist them in changing their old habits. It was also found that many people do not know that water can be responsible for spreading sickness. Therefore, this issue is discussed at great length when necessary. more>>

PET bottles

In recent years, the PET bottle has come under criticism. Particularly on the internet and in emails, rumours have arisen stating that drinking water from PET bottles causes cancer or other diseases. To be certain that the SODIS method has no dangerous side effects for those who use it, Federal Laboratories for Materials Testing and Research (Empa) tested the use of PET bottles. Empa confirms that when the SODIS method is applied correctly, a threat to health does not exist. more>>

Scientific publications: Microbiology, Health, Training strategies, PET bottles

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Clean drinking water in 6 hours

Clean drinking water in 6 hours

Important points to consider when applying the SODIS method

Material, colour and shape of the bottle

Turbidity

Cloudiness

Rain

Preventing recontamination

Research

Microbiology

Health

Training strategies

PET bottles