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How to purify water with sunlight only
Here are some details about purifying water with sunlight. Water can be disinfected with a bottle of
Pepsi or any other soda and sunlight. This method kills all pathogenic microorganisms and makes the
water drinkable but do not remove any minerals from the water (hard water still will be hard after the
process). It is safe we tested it last year with our Bible Institute students and with two laboratories.
All its needed is a bottle of PET (PolyEthylene Terephtalate) (a plastic bottle of soda), 1 wash the bottle
the first time you use it. 2 Fill 3/4 of the bottle with the water, 3 close the bottle and shake it for 20
seconds (to air the water), 5 fill the bottle completely and close it tight. 6 Place the bottle on a roof, on
the concrete, on top of a vehicle or wherever it will be exposed to the sun for six hours, AFTER 6
HOURS the water is free of pathogenic microorganisms. Ready for human consumption. I believe this
method will be great to use in disasters like Louisiana and Mississippi in 2005.
If the water is not clear
If the turbidity of the water is too much (if you can not see your hand through the bottle with water)
use a piece of clean cloth to filter the water before you put it to the sun.
The Solar Water Disinfection (SODIS) process is a simple technology used to improve the
microbiological quality of drinking water. SODIS uses solar radiation to destroy pathogenic
microorganisms which cause water borne diseases.
SODIS is ideal to treat small quantities of water. Contaminated water is filled into transparent plastic
bottles and exposed to full sunlight for six hours.
Sunlight is treating the contaminated water through two synergetic mechanisms: Radiation in the
spectrum of UV-A (wavelength 320-400nm) and increased water temperature. If the water
temperatures raises above 50°C, the disinfection process is three times faster.SODIS requires sun
radiation and temperature: the container needs to be exposed to the sun for 6 hours if the sky is
bright or up to 50% cloudy the container needs to be exposed to the sun for 2 consecutive days if the
sky is 100% cloudy, during days of continuous rainfall, SODIS does not perform satisfactorily.
Rainwater harvesting is recommended during these days.
If a water temperature of at least 50°C is reached, an exposure time of 1 hour is sufficient
Suspended particles in the water reduce the penetration of solar radiation into the water and protect
microorganisms from being irradiated. SODIS requires relatively clear water with a turbidity less than
30 NTU. In water with higher turbidity than 30 NTU pathogens will have to be inactivated by the
temperature rather than radiation (>50°C for at least an hour) or the water has to be filtered before
being exposed to the sun.
Material and Shape of the Containers
Various types of transparent plastic materials are good transmitters of light in the UV and visible range
of the solar spectrum. Plastic bottles made from PET (PolyEthylene Terephtalate) are preferred because
they contain less UV-stabilisators than PVC (PolyVinylChloride) bottles.
How to distinguish PET and PVC: Bottles of PVC often have a bluish gleam. If PVC is burnt, the smell of
the smoke is pungent, whereas the smell of PET is sweet.
Aged bottles
Ageing of plastic bottles (due to mechanical scratches and due to photoproducts) leads to a reduction
of UV transmittance which will reduce the efficiency of SODIS. Heavily scratched or old, blind bottles
should be replaced.
Migration of organic compounds
the migration of organic compounds from reused and new PET Bottles into the water was examined by
a team of researchers from the EMPA (Swiss Federal Laboratories for Materials Testing and Research).
Adipate and phtalate such as DEHA and DEHP were detected in very low concentrations - the level of
concentrations found in the water of reused and new PET-bottles were in the same magnitude as the
concentrations of phtalate and adipate generally found in high quality tap water.
Shape of Containers: UV radiation is reduced by increasing water depth. At a water depth of 10cm and
moderate turbidity of 26 NTU, UV-A radiation is reduced to 50%. This means that PET bottles do not
have the most efficient shape for SODIS as they have a small area for sunlight exposure and have a
water depth of 6-10cm. Containers with a larger exposed area per water volume would be more
efficient. However, PET soft drink bottles are often easily available and thus more practical for the
SODIS application.
Oxygen
SODIS is more efficient in water containing high levels of oxygen: Sunlight produces highly reactive
forms of oxygen (oxygen free radicals and hydrogen peroxides) in the water. These reactive forms of
oxygen kill the microorganisms.
=> Aeration of the water can be achieved by shaking the 3/4 filled containers for about 20 secondes
before they are filled completely.
This method was devised by a Swiss organisations called SODIS. You can find it at www.sodis.ch
Here are some details about purifying water with sunlight. Water can be disinfected with a bottle of
Pepsi or any other soda and sunlight. This method kills all pathogenic microorganisms and makes the
water drinkable but do not remove any minerals from the water (hard water still will be hard after the
process). It is safe we tested it last year with our Bible Institute students and with two laboratories.
All its needed is a bottle of PET (PolyEthylene Terephtalate) (a plastic bottle of soda), 1 wash the bottle
the first time you use it. 2 Fill 3/4 of the bottle with the water, 3 close the bottle and shake it for 20
seconds (to air the water), 5 fill the bottle completely and close it tight. 6 Place the bottle on a roof, on
the concrete, on top of a vehicle or wherever it will be exposed to the sun for six hours, AFTER 6
HOURS the water is free of pathogenic microorganisms. Ready for human consumption. I believe this
method will be great to use in disasters like Louisiana and Mississippi in 2005.
If the water is not clear
If the turbidity of the water is too much (if you can not see your hand through the bottle with water)
use a piece of clean cloth to filter the water before you put it to the sun.
The Solar Water Disinfection (SODIS) process is a simple technology used to improve the
microbiological quality of drinking water. SODIS uses solar radiation to destroy pathogenic
microorganisms which cause water borne diseases.
SODIS is ideal to treat small quantities of water. Contaminated water is filled into transparent plastic
bottles and exposed to full sunlight for six hours.
Sunlight is treating the contaminated water through two synergetic mechanisms: Radiation in the
spectrum of UV-A (wavelength 320-400nm) and increased water temperature. If the water
temperatures raises above 50°C, the disinfection process is three times faster.SODIS requires sun
radiation and temperature: the container needs to be exposed to the sun for 6 hours if the sky is
bright or up to 50% cloudy the container needs to be exposed to the sun for 2 consecutive days if the
sky is 100% cloudy, during days of continuous rainfall, SODIS does not perform satisfactorily.
Rainwater harvesting is recommended during these days.
If a water temperature of at least 50°C is reached, an exposure time of 1 hour is sufficient
Suspended particles in the water reduce the penetration of solar radiation into the water and protect
microorganisms from being irradiated. SODIS requires relatively clear water with a turbidity less than
30 NTU. In water with higher turbidity than 30 NTU pathogens will have to be inactivated by the
temperature rather than radiation (>50°C for at least an hour) or the water has to be filtered before
being exposed to the sun.
Material and Shape of the Containers
Various types of transparent plastic materials are good transmitters of light in the UV and visible range
of the solar spectrum. Plastic bottles made from PET (PolyEthylene Terephtalate) are preferred because
they contain less UV-stabilisators than PVC (PolyVinylChloride) bottles.
How to distinguish PET and PVC: Bottles of PVC often have a bluish gleam. If PVC is burnt, the smell of
the smoke is pungent, whereas the smell of PET is sweet.
Aged bottles
Ageing of plastic bottles (due to mechanical scratches and due to photoproducts) leads to a reduction
of UV transmittance which will reduce the efficiency of SODIS. Heavily scratched or old, blind bottles
should be replaced.
Migration of organic compounds
the migration of organic compounds from reused and new PET Bottles into the water was examined by
a team of researchers from the EMPA (Swiss Federal Laboratories for Materials Testing and Research).
Adipate and phtalate such as DEHA and DEHP were detected in very low concentrations - the level of
concentrations found in the water of reused and new PET-bottles were in the same magnitude as the
concentrations of phtalate and adipate generally found in high quality tap water.
Shape of Containers: UV radiation is reduced by increasing water depth. At a water depth of 10cm and
moderate turbidity of 26 NTU, UV-A radiation is reduced to 50%. This means that PET bottles do not
have the most efficient shape for SODIS as they have a small area for sunlight exposure and have a
water depth of 6-10cm. Containers with a larger exposed area per water volume would be more
efficient. However, PET soft drink bottles are often easily available and thus more practical for the
SODIS application.
Oxygen
SODIS is more efficient in water containing high levels of oxygen: Sunlight produces highly reactive
forms of oxygen (oxygen free radicals and hydrogen peroxides) in the water. These reactive forms of
oxygen kill the microorganisms.
=> Aeration of the water can be achieved by shaking the 3/4 filled containers for about 20 secondes
before they are filled completely.
This method was devised by a Swiss organisations called SODIS. You can find it at www.sodis.ch