How does it work?
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)
If the water is very turbid, the effectiveness of the
method is reduced. It is very easy to determine whether the water is
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 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
Factsheet Cloudiness (EN, FR, ES)
The method does not work satisfactorily during lengthy
periods of rain. On these days, we recommend collecting rainwater.
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.
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© SODIS 2014
Last update: 24.05.2011
An initiative of
Swiss Federal Institute of
Aquatic Science and Technology