The Nadi Filter

If you’ve been following my blog you may have read a while back about Rus Alit who is well known for his work helping communities to get clean water through appropriate technologies.  If you didn’t read that article appropriate technology is any technology that is simple and doesn’t use any outside energy source like fuel or electricity and uses materials that are available locally and can be made locally.  I had never heard about appropriate technology before writing the article about Rus, but it immediately made so much sense to me.  Go to where the problem is and come up with a solution that the people can make and maintain themselves.  This does two things; one, gives people a sense that they’re doing something to help their family or community which, if nothing else, makes people feel good.  Second, if people in a community help to make this technology they can then teach others to make it, as well as be able to maintain the system themselves.  As cliché as it is, it made me think of the saying “if you give a person a fish they eat for a night, if you teach him to fish he’ll have food forever”.  So with that in mind let’s take a look at the Nadi filter.

A nadi is basically a clay pot that has been used for storage in many countries for centuries and is the main component of the filter.  You start with a 30-35” tall nadi and make a hole in the side of it about 20” off of the ground.  You then put a piece of flexible pipe through the whole in the side with one end reaching the bottom of the nadi and the other end protruding out of the side, and then seal around the whole in the side of the nadi.  From here you basically are adding stones and sand.  Layer 1 (bottom layer) is one layer of “potato sized” rocks.  The gaps between these larger rocks will let water flow between them and into the pipe.  From here you add successive layers of smaller rocks.  For the second layer you use smaller stones that will help fill the gaps between the potato rocks, but will also keep the smaller rocks in layer three from slipping through.  Layer 3 is smaller gravel rocks, followed on layer 4 with seed sized rocks.  On top of layer 4 you then place sand until you’re about five inches below where the pipe exits the filter.  At this point you get a mutca, which is a best described as another clay pot that goes on top of the nadi, and put a nail sized hole it.  This is what you pour the water into, and the nail sized hole lets it slowly drain into the nadi.  The last step is to put a cloth over the top of the nadi, place the mutca on top of it, and then tie the mutca to the nadi.  That’s it!  It’s so simple and once you have the materials it can be put together quickly and you can be drinking clean water in no time.

So how does rock and sand filter the water?  It’s all about biology.  There are “good” microbes and “bad” microbes.  The bad microbes are what cause disease and bacteria.  This filter works by giving the good microbes a place where they can set up a home and reproduce; the sand.  Because the sand has so much surface area in all the little pieces it gives a lot of room for the good microbes to hold onto and grow.  As time goes on the microbes continue to multiply on the sand.  After about 3 weeks there are enough good microbes eating the bad microbes for the water to be considered very clean and good to drink.  Then all you have to do is add dirty water to give the good microbes a supply of food (the bad microbes), and what comes out is clean water.

reduced to less than 1, faecal coliforms reduced by 95-100%, often landing a little over 99%, viruses are usually reduced by 100%, the level of organic material purified is lowered by 60-75%, iron and magnesium are largely removed, and the level of heavy metals is reduced anywhere from 35-95%.  What this is saying is that within a day you can build a filter that will give you some very clean water with fewer parasites, viruses, bacteria and chemicals then what you would normally drink.  How much does this cost?  The report that I saw said that the filters typically cost 450 Indian Rupees, which is about $8.71 USD.

So there you have it, the Nadi filter; low cost, easy to make, locally available materials, and ultimately clean water.  That is what appropriate technology is all about.  Every time I read about an appropriate technology it makes me think about companies spending a lot of money to develop things like water filtration systems of all different types and sizes, but then you also have a water filtration system that is under $10 and can basically be built with things found on the ground by someone in the middle of no where.  By making them easy to make and maintain you have ultimately given someone clean water for life and enabled them to teach others how to make the same which as far as I’m concerned is the best way to do it.

 

The Nadi Filter
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5 thoughts on “The Nadi Filter

  • October 9, 2012 at 10:31 am
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    Thanks for sharing our Nadi filter technology on your site, hope you will also keep sharing the info, how much people attracted and can support our this effort for promotion this technology in other developing countries.
    looking for your reply
    from: Khurshid Bhatti, president/CEO, Association for Humanitarian Development (AHD) Hyderabad Sindh Pakistan Ph: +92-22-3860880 email: ahdpak@gmail.com info@ahdpak.org

    Reply
    • October 15, 2012 at 9:04 pm
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      Hi Khurshid,
      Thanks for the comment. Please email me directly at hydratelife@gmail.com and we can talk more.

      Regards,
      Brian

      Reply
  • September 27, 2013 at 2:38 am
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    We are Trading company here South Korea,
    Sir we can arrange Water filter for make clean water for peoples health.
    if i can help in this line then sure i will do my best with out any charge, i comments no for business only help to company who working for this projects.
    thanks
    regard
    M.ARFAN ALI

    Reply
    • October 3, 2013 at 6:50 pm
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      Thank you for your comment. Can you give me a little more information about your water filters? You can email the information to me at hydratelife@gmail.com.

      Regards,
      Brian

      Reply
  • June 22, 2016 at 6:50 pm
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    very neat and very smart! I wonder how much water a Nadi as described will process over 1 day? Trevor

    Reply

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