|Home-made biological water filter
What if you don’t have any clay
Ideally filters are both home-made and biological. This is still
possible where clay pots or other materials needed for this filter are not
available, by making adaptations. For example in the place of clay pots concrete
pots are used which can easily be made.
Warwick University has a simple way for people to make their own
concrete pots: Download Ferro-Cement Jar Instructions [PDF format - 550 Kb]
In civil public health emergencies effective filters can be built
in situ with bricks or broken paving slabs and cement mortar.
Below are guidelines for making adaptations without reducing the
performance of the filter.
Advocates of the filter support appropriate technology that not
only can be maintained locally, but can be made by the families themselves, with
materials they can afford and easily get hold of, and can be replicated by other
By making the necessary adaptations to the materials used, more
people will be able to become self sufficient at making biological
This is valuable because uneducated and disempowered people are
vulnerable to the tendency to become passive recipients of help from development
This tendency can be reinforced more and more by each project
introduced that does not work on a self-help basis.
With a home-made filter people’s self sufficiency increases so
they don’t add to or suffer from market forces.
The design is easy to replicate and it is cheap enough for people
to afford themselves so it will make them feel richer and more able as they make
their own filter with materials they already have access to.
It will therefore strengthen the values that help people who are
vulnerable to consumerist aspects of development: valuing the responsibility to
overcome our own problems; valuing what we already have; valuing knowledge we
can share with others; our health.
As long as adaptations do not contravene the principles and
instructions below that safeguard the beneficial biology and function of the
filter, highly effective home-made biological filters can be made using the
locally available materials.
Once filters with the adaptations have been tested, filter teacher
training projects can be setup to pass on the adapted design to the local
Concept and principles for making adaptations, to be read with the
Materials used must be locally available and ideally familiar to
the families who need to make biological filters.
The filter must produce the controlled and protected environment
needed for sufficient beneficial biology to colonize it.
The features key to the well being of the beneficial biology and
functioning of the filter are as follows:
- An even drainage provided by the layers of stones and gravel below the sand. This is so that no water takes a short cut and it all slowly passes as many beneficial microbes as possible that live on the surface of the sand grains.
- Sufficient depth of sand 12 inches. This provides enough homes for the beneficial biology.
- The inside diameter of the filter should be 10 to 14 inches. (This allows approximately 15 liters to pass through in the first 30 minutes)
- A hose with no joins or splits. This provides an outlet for the clean water and reliably prevents water from becoming re-contaminated as it rises up and out.
- The hose outlet must be 5 inches above the top of the sand.
- The beneficial microbes are aquatic so the sand must always be under water.
- The beneficial biology on the surface of the sand must not be disturbed by the water flowing in.
- 5 inches insures that the water level is maintained above the sand allowing an inch for if the filter is not make accurately, 1.5 inches for evaporation and 2.5 inches depth of water to provides a buffer zone preventing water flowing in from churning up the sand and upsetting the service beneficial biology.
- A hole in the main container at this level needs only a low pressure seal which is easy to achieve and also any leaks are slower and of less significance.
- A poor seal here does not threaten to re-contaminate the filtered water.
- The top pot should have one small hole of the diameter of a typical 3 inch nail. This prevents water flowing into the filter too fast so the top layer of sand is not disturbed.
- The bottom of the top pot and the top of the filter pot should be 10 to 12 inches above the level the pipe exits the filter. This provides the water pressure to drive the filter.
- The top pot must be fixed in place to prevent the sand being tampered with.
- The clean water must be protected from recontamination.
- A light weight cloth over the top pot acts as a screen to prevent leaves blocking the small hole.
- There should be a gap between the top pot and the filter to let in oxygen. This also means that the water flowing in can be seen allowing a blockage in the small hole to be notices if it occurs.