Science
Using the sun to sterilize water

 41417032 Rose203Clever way to purify water – “Tanzanian villagers have begun using an energy-saving method to sterilise their drinking water – leaving the water under the sun. About 40 houses in Ndolela are using solar purification. Mrs Longwa says the process is simple to follow. “I fill the plastic bottles, put the lids on, then put them on my black-painted roof where they stay for a whole day.” The sun heats the water, helped by the black roof, which helps to absorb the heat. Solar radiation means a combination of ultra-violet rays and heat destroys the bacteria which cause common water-borne diseases like cholera, typhoid, dysentery and diarrhoea. After eight hours in the sun, it is ready to drink.” [via] – Link.

16 thoughts on “Using the sun to sterilize water

  1. Pretty clever. However, there is concern about chemicals leaked from the plastic bottles as they heat. Plastic water bottles leak chemicals even at room temperature. Of course this is the much lesser of the too evils. I would much rather drink sterilized water from this solution than the alternative…

  2. radiorental, I believe you’ve missed one point in the article. With this method, it would normally take 8 hours to purify the water; that’s at temperatures less than 50°C. However the time may be reduced to only one hour if they are able to achieve & sustain 50°C or more. Even if the air temperature isn’t that hot, it is still easy to achieve that kind of heat using the method described, which is essentially a solar oven.

    Perhaps through using a combination of sari cloth filters, this solar technique, and the use of brass pots to store water, water-borne diseases could be drastically reduced.

  3. This is a very interesting low-tech solution to a problem that is pretty much universal in Africa and other parts of the third world. Potable water is a necessity that none of us can survive without and in many African nations the primary cause of disease is trophozoite cysts transmitted trough drinking water consumption. These are a number of microorganisms which will result in Amoebic dysentery. Nothing fun and it can be fatal to imunocompromised individuals, children or the elderly. This is a way of life for many people all around the globe, simple solutions which provide clean drinking water would help break the cycle of poverty and violence in these places.

    A solar cooker for water needs to maintain a constant temperature of 55° C for 60 minutes to reliable kill trophozoite cysts (50° C may result in clean water, but the jury is still out). While this is possible with a low tech solar cooker solution like this, I would argue that its not reliable because there is little chance that a constant high temperature of 55° C will be maintained for the extended period of time required. One passing cloud would cause a resultant dip in temperature.

    Another option is to filter water. The easiest way to accomplish this for most communities it to make use of an aquifer and dig a well. This organization does an excellent job of helping people source and maintain clean water for themselves. The technology they use is time tested, easy to maintain, easy to build, and provides a reliable source of clean water.

  4. Actually, I wouldn’t put much stock into the leaching of chemicals from plastic where food-grade plastic is used. You can find out more about this urban myth all over the internet.

    As for making the water potable, I too am a skeptic. I’d want to see some actual test results before I got too excited.

  5. Check out this introduction article on Water:
    Water
    1.Location
    2.Definitions
    3.Importance in history
    4.Uses of water
    5.Health

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