Solar Water Disinfection

  1. Lloyd Tackitt
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    Jason, known as The Old Man to his colleagues and friends,was talking to his associate, Craig. Jason had recently returned from an extended trip overseas where he had been visiting several third world countries. Jason was a reporter; he had been a reporter for over forty
    years. Jason and Craig had been talking about the trip and Jason mentioned that the World Health Organization (WHO) had shown him a trick or two while he was in Africa.

    "Like what?" Craig asked.

    "Like making safe drinking water with nothing more than a plastic bottle and sunlight."

    "You mean a water still or a solar box. Nothing new about those,"Craig replied.

    "No, not a water still. Not a solar box. Both of those are excellent to know how to make and use, but there is another method that is so simple you'll scratch your head and wonder "Is that all there is to it?" I know I did.The answer is yes, it is that simple. Put water into a clear plastic PET type bottle and set it in the sun for six hours."

    "Really? That's it?"

    "Yes and no,"Jason answered. "On average it is that simple, but as in all things in life there are
    variables. Depending on your distance from the equator it can take more time. It also depends on the temperature of the air; it will work in cool weather but takes a bit longer than in hot weather. If the sky is 50% or more overcast it takes two days of exposure. Doesn't work at night or in a fog or when it's raining."

    "So what's the trick? What makes this work?" Craig settled into a chair, he was interested now and was going into analysis mode.

    Jason gathered his thoughts while lighting his pipe."It's pretty easy to explain. Ever had a sunburn?"

    "Sure, who hasn't?"

    "The sun puts out a wide spectrum of light frequencies. The damage to your skin, the sun burn, is caused by the ultra-violet spectrum. Those rays cause a lot of damage to tissue. They also kill germs the same way they kill skin cells. By putting water into clear bottles in sunlight, you set up a situation where the germs are exposed to the UV rays and die. In average circumstances that takes only about six hours. The best way is to lay the bottles on a roof top facing the sun,the UV rays lose effectiveness if they have to travel more than four inches through clear water, so you lay the bottle where the sun penetrates through the narrow width of the bottle. Stand them up and it doesn't work nearly as well. Up to a three liter bottle works, but bigger than that doesn't.

    "Also it's best to first fill the bottle only three-fourths full, put the cap on it and shake it vigorously for twenty seconds, then fill it all the way up. This distributes oxygen into the water, and oxygen works in tandem with the UV rays. They explained why, but I don't do
    chemistry. It won't work on cloudy water; the particulate matter blocks the rays. Well it will work on semi cloudy water, but not nearly asvfast. If you can read a newspaper headline through the water bottle it's clear enough. Place the bottle full of water on top of a headline, look down through the opening and if you can read the headline you're good to go. If you can't then you should filter the water first, or let it sit in a pan until the particles settle and skim the clearer water from the top.

    "PET bottles are the kind that you get drinks out of, soda bottles, water bottles, like that. PVC bottles don't work, the chemicals in PVC filter UV rays out and testing has shown that you can pick up harmful chemicals from using it. You can, if you need to, do a burn test on a
    sample bottle.PET burns quickly and easily when it is held in a flame.When it is taken out of the flame, the fire goes out slowly, or it may keep burning. The smoke smells sweet. PVC does not burn easily. The material does not burn at all when not in the flame. PVC smoke smells acrid."

    "What about chemicals from the plastic leaching into the water? There's been a lot of talk about that lately,"Craig asked.

    "Not a problem. The WHO has done extensive scientific studying on that PET and say that the extremely tiny amount of chemical leaching is far below the danger threshold, way below it. By the way,bottles with color tinting in them don't work, doesn't let the UV through."

    "What about glass bottles? I know glass blocks UV also."

    Jason smiled. "You're right to an extent. Clear glass jars will work, but it takes longer, all day. Plastic sandwich bags work as well as PET bottles, although they tend to leak a bit."

    Craig thought about it for a moment. "It really is simple isn't it?"

    "Very simple. I started carrying two dozen sandwich bags in my overnight bag. Just in case. They take very little space and once or twice when I was in an area where the water was suspect I used them, and never got sick once. But, you should also know that this only disinfects for germs. Any chemical contamination is still in the water, heavy metals, pesticides, things like that are not affected.

    "But, now you know a simple and effective method of making sure you have safe drinking water. Next time you're caught in New Orleans after a Hurricane like you were after Katrina, keep it in mind. It might save your life."

    For further in-depth reading: www.sodis.ch/index_EN

    Lloyd Tackitt is the author of A Distant Eden.​

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