biosand water filters

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How to Build a Water Filter

During water training, we would start at 9:00 every day and head up the “water filter learning center” (the chapel.) We would discuss the topics of clean water and sanitation, and then get in groups and talk about what we learned the day before. It was nice working with many of the people there; the only thing I didn’t like was the way I had to step aside sometimes so the girls at the Lugulu Girl’s School could learn more. Because they are planning to start producing the filters soon, I felt like I learned a little less. But other than that, I thought that they training was perfect.

Water is unclean right now in many place in Africa

This is because when people decide that they need to wash clothes, the soap gets into the water. Also animals “go” in the river, and all of that soap and waste gets into the drinking water. They also commonly use fresh manure to fertilize their gardens, instead of waiting six months for it to compost properly. These are only a few of the ways that water gets dirty, why filtering is so important.

It’s important to have these filters so that the community can create a sustainable project- the water filter business- and have clean water.

How it works:

The filter makes the water clean because the bacteria on the top layer of water in the filter kills the bacteria in the water, and then it filters through the sand slowly and then goes through the pipe and out through the spout. The sand catches the virus molecules so that they’re no longer in the water.

Stolen bolts

When building your water filter, make sure you have all of the things you need. What happened to us was that someone stole all of the nuts and bolts from the molds. We were forced to painstakingly hand drill bigger holes in the molds to fit the bolts we had. Make sure you store your materials in a secure place.

Below I have included a step-by-step guide to making the water filters, for anyone who is interested in the details.

Step One: Get sand, gravel, and cement. Take the sand and sift it ALL, until it’s all sifted. Then get an army of washers, and start washing the sand. And washing, and washing, and washing. Wash it until the water is clear, or almost clear. When you put some of it in a jar, you need to be able to see your finger through the jar within 5 seconds.  Otherwise, you guessed it, wash it again…and again…and again.  Then, make sure you’ve washed enough of ¼ inch sized gravel, and ½ inch sized gravel.

Step Two: You will assemble the filter mold. To assemble it, first “Kimbo it up!” (Kimbo is an African brand of cooking grease.) You put the Kimbo on so that the concrete won’t get stuck to the mold.

Step Three: Then, take the pieces and bolt them together, upside down. Now bring the sand and gravel the you washed.

Here’s the recipe for the concrete:

Two parts washed sand

One part ¼ inch gravel

One part ½ inch gravel

One part concrete mix

Slowly mix the sand and gravel together. Then add the concrete mix. Warning: Do not breathe in the concrete mix. Add water slowly to the mixture, but not too much, until it’s like a gravelly paste. Not like liquid concrete- a nice, gravely paste.

Step Four: Get some pipe that is pretty thin, like the width of a pencil. Get about two yards of it, just in case. Stick it into the mould so it comes out where the spout of the filter will be, with an inch sticking out. Then, tape the end of the pipe that’s in the mold and get a piece of metal that’s pretty thin. Bend it so it’s a right angle. Then, tape the piece of metal down on the top of the mold, and stick the pipe underneath it. Tape the pipe down too.

Step Five: Take your concrete mixture, and with a shovel and shovel it in. Have two people with sticks mushing the concrete mixture in. Make sure the pipe you inserted doesn’t touch either side of the mold, but is right in the middle. Then take a rubber mallet and bang the sides, so that all of the air bubbles in the concrete rise to the top. Let it harden for a day.

Step Six: Flip the mold right side up. Unbolt it and take the spout side off first. Then, if there are no cracks in the filter, you don’t need to add any more  concrete. Fill the filter with water. It should come out the pipe, and you will be able to see if there are any holes that you need to fill because the water will leak out. If there aren’t, let the filter cure for seven days and seven nights.

Step Seven: Take your finished filter, and with the sand and gravel that you washed previously, fill the water filter, staring with the ½ inch gravel. You need about two inches of it at the bottom of your filter. Then fill it with another two inches of ¼ inch gravel. Next, fill it with sand up to the last five inches of the filter.

Step eight: Assemble the diffuser plate by getting a square, thin piece of metal, an punch holes into it in a grid pattern. Put it into the filter. Now fill the filter with water, leaving two inches of air. Then you are done.

Throw a round of water in it and drink up!

Well actually, you need to pour water in each day for several days to grow enough bacteria in the water at the top of the filter to be able to purify the water, but THEN…

Throw a round of water in and drink up!!

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Posted on: December 21, 2010 | Categories: Kenya, Water



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