Genius Breakthrough In Making Water Potable: Plain Old Plastic Bottles

Leaving water out in a clear bottle in the sun is a free and easy way to kill pathogens. Now it's time to let the people who bad water is killing know that the solution is at their fingertips.

plastic water bottle

Researchers in developing countries have discovered a free nuclear fusion-powered way to clean polluted water and kill disease-causing organisms. It's called the "sun" and it's available to anyone with relatively clear skies and a few plastic water bottles. Although first identified in the 1980s, researchers have been perfecting the technique—known as SODIS for solar water disinfection—and preaching its virtues around the world.

"The number of people regularly using SODIS for the treatment of their drinking water is steadily increasing," says Regula Meierhofer of the Swiss Government's Department of Water and Sanitation in Developing Countries, one of the groups most active promoting the idea. Today, at least 5 million people in about 30 countries disinfect their drinking water daily with SODIS, and 750,000 more join the ranks each year. SODIS works by exposing contaminated water to the sun's UV rays, destroying the genetic material and cellular structure of viruses, bacteria, and protozoa. PET plastic bottles work best, as they're both durable and allow much of the UV radiation to pass through them. Bottled water is left outside for at least six hours (or 48 hours if it's cloudy), and then stored for future use. Since both polluted water and plastic bottles are abundant in many developing countries, SODIS is catching on and cutting the incidence of diarrhea by more than 85% in some places.

But that's still just a drop in the proverbial bucket. At least 1.2 billion people are without clean water globally, and 1.8 million children die each year from diarrhea (often water-borne), the combined population under the age of 5 in New York and London, according to a study for the Swiss Government by Urs Heierli.

So why isn't a cheap, practical and effective solution not an instant success? Heierli rephrased the question in a more telling way in his report: "Why is it so hard to get safe water to the poor—and so profitable to sell it to the rich?"

Basically, it's a marketing problem. Even in places where SODIS training is readily available, only about half of the households trained in the technique actually adopt it. SODIS training cannot be stopped after the first year of promotion. "People need reminders to form solid habits," says Meierhofer. They also need to be convinced of its value: Families capable of spending the modest time and money for SODIS often prioritize other things (such as buying soft drinks).

If SODIS and comparable treatment methods such as boiling, sand or ceramic filtration, and chlorination, can finally gain traction, it's a safe bet that a profitable business model will be needed to solve the problem, argues Heierli. He suggests a sustainable supply chain, massive demand catalyzed through social marketing campaigns, and some good old fashioned salesmanship. Hopefully, those without clean water will soon be able to drink to that.

[Image: Flickr user marcelometal]

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  • Dr.Anumakonda Jagadeesh

    method suffers from some drawbacks. The PET Bottles get scratches which lessens
    the transmittance of sunlight. When put it open dust accumulates in the groves
    of the PET Bottles. There is a warning printed on the PET Bottles in India, CRUSH
    THE BOTTLE AFTER USE. Moreover if one uses PET bottles for longer time there
    will be brown colour formation inside bottom. A Chemical DAHE in the PET Bottle
    is not safe.

    When the PET bottles are put in open there is the WIND EFFECT which reduces the

    Both UV and Thermal are needed for eradication of bacteria.

    50 degrees Celsius is the crucial.

    I have refined the method by using Glass Bottles(Clear ) which are available in
    India at about 1 Cent(Used wine bottles).

    The innovative solar disinfection system has a wooden frame of length 2
    ft,width 1 foot and depth 6 inches with bottom sinusoidal shaped polished
    stainless steel (curvature slightly larger than standard glass wine bottles,
    about 5 inches diameter) . On the front is fixed a glass sheet having lifting
    arrangement with a knob (this glass enclosure will protect the glass bottles
    from cooling down due to outside wind). There are screws which can be used to
    keep the contents airtight. On the backside a stand is fixed which will help
    the unit to be placed according to the latitude of the place for maximum solar
    In this method clear glass bottles (used wine bottles) are utilised instead of
    PET bottles as the former are easy to clean, lasts longer and are available at
    a low cost in India.
    Solar disinfection 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 water is achieved by shaking the 3/4 water filled
    bottles for about 20 seconds before they are filled completely.

    The unit has an advantage in that the rear reflection stainless steel will pass
    the light through the bottles a second time, to both increase exposure and
    eliminate shadowing. This reflection system will increase the light intensity
    minimum 2 times.
    It has been widely experimented and established by earlier researchers that at
    temperature of 50C (122F), pathogenic microbes are inactivated. The temperatures
    which cause approximately a 1-log decrease in viability with 1 min are 55C
    (131F) for protozoan cysts; 60C (140F) for E.coli, enteric bacteria, and
    rotavirus; and 65C (149F) for hepatitis A virus .Negar Safapour and Robert
    H.Metcalf in their extensive studies reported enhancement of solar water
    pasteurization with reflectors and the crucial role of temperature above 50C
    (122F) in the elimination of pathogens.


    The unit is placed in the south direction (in India) around 9 am with inclination
    equal to the latitude of the place. The glass bottles are filled with water
    three fourths and shaken for 20 seconds to generate oxygen and then completely
    filled. The water filled bottles are fixed with caps and put in the groves of
    the solar disinfection unit. The glass door is closed and clipped airtight.
    Water bottles are removed from the unit at 4 pm and taken to a cool place and
    the disinfected water transferred to a clean vessel, covered for later usage.

    Suspended particles in the water reduce the penetration of solar radiation into
    the water and protect microorganisms from being irradiated. Solar disinfection
    requires relatively clear water with a turbidity less than 30 NTU.To remove
    turbidity traditional methods of putting the paste from seed of strichnos potatorum (Nirmal seeds) by
    rubbing the seed on a rough stone with water is used. The method is effective,
    turbidity settles down in half of an hour and the seed are available in plenty
    in forests in India
    besides being inexpensive.

    This Kit is modular. Larger size (Community) water disinfection systems of 100
    litres can be made.

     This cost effective, simple and Innovative
    system is expected to be a moon for developing countries rural areas.

    Dr.A.Jagadeesh Nellore (AP), India

    E-mail: anumakonda.jagadeeshgmail .com

  • Matthew Fuller

    This is an activity of the Water and Sanitation program here at Peace Corps/Peru as well.  We've had the same trouble with families adopting the technique.  When given the option, many prefer boiling water as that's what they're used to.  But the families who do regularly practice with SODIS like that it's easier to do, and if they do it regularly they always have fresh water on hand  to drink and don't have to wait for the water to boil AND cool.  Families with small children seem to adopt this practice more so than any other.  Independent lab work shows no traces of PET contamination, and we tell families to replace the bottles when they look less than fresh.

  • Michael J. Coren

    Interesting study on chemical risk from this technique here:
    Conclusion: The traces of the plasticizers DEHA and DEHP leaching  from PET bottles upon SODIS (solar water disinfection) treatment do not pose a significant cancer risk and are below the respective limits for drinking water fixed by the WHO.

  • Jamil Buie

    My grand father taught me to always take a large zip lock bag with me. In lieu of a bottle where the diameter is about 4 inches. Fill the ziploc so it is about 3/4ths of an inch and lay it on an even flat surface. Same deal but renders faster. 
    Mick, I hear you but your point is akin to a starving man refusing to eat a ham sandwich with mayo on it because he is Muslim, Vegan or concerned about his cholesterol the focus is sustaining yourself right now. The chemicals are not good but I am fairly certain dehydration and death are worse.

  • Dr.Anumakonda Jagadeesh

    Dear Jamil Buie:

    It works. Actually the solar disinfection efficiency depends on the depth of the water in the container exposed. But Plastic bags in most cases produce smell and as such people may not like the water disinfected . That is why I used Glass Bottles. In our System we tested 50 samples of waste water,bore water,well water etc., and the purification is 99.9%. The 12 liter system costs around 25 US$ and can be fabricated locally.

    Dr.A.Jagadeesh  Nellore(AP),India

  • mick russom

    Plastics and ultraviolet = toxic chemicals. used over time these compounds are estrogenic and disrupt hormones. They also bio-accumulate. Bad idea. 

  • Dr.Anumakonda Jagadeesh

    You will find answers to your questions in my comments appearing here.

    Dr.A.Jagadeesh  Nellore(AP),India

  • Tim

    I have to agree with Jamil.  Based on the circumstances, the afore mentioned 1.2 billion people are living in.  It takes 3 days to die from dehydration, and less than that to die from dysentery.  Estrogenic hormones don't kill you, at all.  Good call, and way to be health conscious!  (I use a metal water bottle for this very reason)  But, in this case, I think they should drink.

    On a related note in support of the article: Last summer I went to Haiti for a week to help with missions/child-support work.  It was post earth quake by several months, but the devasted infrastructure had not even begun to heal.  There were plastic bottles by the tens of thousands littering the streets, sewers, rivers, and anywhere else rainwater pushed them.  The SODIS strategy for creating clean water caught me by surprise but gave me a sudden sense of hope!  I didn't realize there was enough UV exposure in 6 hours of clear sun to kill germs in a clear plastic container!  I will pass on this information to make sure it is known where it might do some good.

  • Kelly Wilson

    With so many advisories about NOT reusing water bottles because they create bacteria I can't see how this would work.  Only half the bottles would be usable and to be usable they would have to NOT contain a single bend or ding.  Apparently that is was causes those bottles to accumulate bacteria.  Google my info if you disagree and see what I mean.

  • Dr.Anumakonda Jagadeesh

    Please read my comments published here.

    Dr.A.Jagadeesh  Nellore(AP),India

  • Stuart Bogue

    The bacteria are created and exist sitting on a shelf in a room or in a refrigerated bottle etc. Placing the bottle and bacteria in the sun kills the bacteria in the water,no matter from where it originated...