Safe water through sustainable practices: The slow sand filter

Posted on July 27, 2008 by Orpheus

First; my humble apologies for being so slow to moderate comments. Vast improvement is in order. We have updated the software that runs the blog ( as of July 24 2009) which went perfectly. Moderating should be quicker now.

The slow sand filter works using biological processes. Water passes through a layer of sand and after about 3 weeks a layer of biological activity forms in the upper 2 to 3 centimeters of the sand. The bacteria in this layer sometimes called the “schmutzdecke” break down harmful bacteria such as “beaver fever cysts”, all coliform including the most deadly and the resulting water out of the filter is safe. A lively discussion about these filters would be very encouraging. Anyone who has comments, questions, or experience with these filters is encouraged to leave comments. The website http://www.shared-source-initiative.com/biosand_filter/biosand.html documents a year and a half of experience building and operating 2 of these filters built from mostly recycled materials. All tests so far have shown they work very well. Also the website http://www.slowsandfilter.org has more detailed information and an FAQ page.

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2 Responses to Safe water through sustainable practices: The slow sand filter

  1. Jon P says:
    December 4, 2009 at 2:38 pm

    Greetings!

    I want to first off and say thank you for not only keeping up the SSF website, but for this blog which will enable people to interact and share ideas about SSF.

    I am in the process of building a few of these filters, but my biggest challenge is finding the right sand. I have made numerous phone calls and countless e-mails looking for silica sand. However, I had a break through once I contacted a local Cemex office which informed me that they would be able to help me out and that they’d put me in touch with a salesperson that could answer specific questions.

    So my advice for those on the hunt: contact local AGGREGATE suppliers. If you live in a large city, such as Houston, there are PLENTY, especially for all the growing construction needs.

    One question however,

    What is the exact mesh size for .15, .25., and .35 sand?

    -Jon

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