Bio-sand water filters
Practical Action
these do not require a mould. The use of a mould makes it difficult to mass produce the filters
as they are made on site on an individual basis.
Operating the filter
The lid in removed,
A bucket of water or other container is poured into the top of the filter.
The diffusion plate slows the force of the water.
Water then travels slowly into the biological layer at the top of the sand.
Water continues slowly through the sand bed.
After passing through both levels of gravel, the water is propelled up and out.
Then treated water is collected in a clean container.
Amount of water treated
Household bio-sand filters typically provide 30 to 60 litres of water per hour, which is
sufficient for a family of five to ten members. The flow rate may decrease over time as the
filter becomes clogged, but can be restored with cleaning.
Contaminant removal
Bio-sand filters have been shown to remove more than 90% of faecal coliform, 100% of
protozoa and helminthes, 95 to 99% of zinc, copper, cadmium, and lead, and all suspended
sediments. Bio-sand filters have also been shown to remove 76 to 91% of arsenic, reducing it
to an acceptable concentration. These filters do not sufficiently remove dissolved compounds
such as salt and fluoride or organic chemicals such as pesticides and fertilizers. The biological
layer’s effectiveness is influenced by temperature. Ammonia oxidation stops below 6° Celsius
and alternative treatment methods are required below 2° Celsius. Additionally, because bio-
sand filters are not able to handle high turbidity, they may become clogged and ineffective
during monsoon or rainy seasons.
Ease of use
Bio-sand filters require daily fillings
during the 2 to 3 weeks when the
biological layer is growing. Bio-sand
filters also require regular cleaning,
which involves agitating the water above
the biological layer. The filter will require
1 to 2 weeks of non-use after agitation to
allow for the regrowth of the biological
layer. On occasion, the sand in the filter
needs to be cleaned as well. There are
several different methods to clean the
sand, though all of them require
significant labour, significant training, or
high cost. User error has also been found
to affect the filter’s efficacy, especially
because of the required 2 to 3 week non-
use period for growing the biological
layer. The users of the filter must have a
maintenance guide (for example, a
plasticized leaf). This guide can be
adhered to the filter or it is possible to
be placed on the wall near the filter.
Figure 5: Bio-sand filters are easy to use. Photo:
Soluciones Prácticas.
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