Technicians, who construct and install the filter, will also provide the sand. They have sieves with different mash size. The householder will always get new sand through the technicians. We found out the literature has very strict figures about it, while in practice it is more important that the sand itself will not contain clay components. Normally ordinary river sand works best.
Sand grain size: before a project is initiated good quality sand should be identified as close to the project area as possible. We have used in most cases river sand. While specific mixtures of sand grain sizes are recommended in various literature, I found that in practice a rather wide variety of sands can be used, as long as a proper mix of grain sizes is available (for instance: only coarse sand without a fine grain content will impair filter action). As most of our projects have been very much low tech, we never used filters or mesh to achieve correct grain size mixtures, but rather experimented a bit with different sand available until a good source was found).
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