Innovation Prize for its contribution to sustainable solutions
for rural drinking water treatment.
What are the CWF components?
1. Filter elements or pots are made in Sri Lanka under
contract in factories situated in Matara and Kelaniya.
Meticulous efforts have been invested in the production
systems to ensure consistent product quality from both
factories.
2. Water receptacle (or buckets) with lid. These are made by
a Kurunegala based producer. The translucent blue colour
differentiates CWFs sold on the commercial market from the
white ones previously distributed free of charge. Each bucket
is branded with the SLRCS logo.
3. A spigot with washers is supplied and instructions are
given to ensure its leak-proof assembly to the bucket.
4. Cleaning brush: A cleaning brush is provided with the clay
water filter kit so that families can regularly clean them.
5. Usage instructions brochure: These instructions help to
educate new users on cleaning and maintenance.
Source: Michael Roberts, 2004
How the CWFs are made in Sri Lanka
The clay pot production equipment consist of hammer mills,
grinders, horizontal mixers, hydraulic presses and other tools
that include moulds, sifters and weigh scales. First, the rice
husks are ground and made ready for mixing. Second, the
husks are mixed with dry clay and water until a homogenous
clay sludge is ready. This clay mixture is then shaped into
blocks and taken to the press area where hydraulic presses
are used to produce the basic pot shape.
At this stage the filter element looks much like an oversized
plant pot. However, it is much more than that as its rich husk
content makes it ideal for filtering contaminated water. These
“green” pots need to be air-dried for 8 -12 days depending on
the ambient temperature and humidity.
A hydraulic press located at Mr. W.
Pothmitiyage’s pottery workshop in Kelaniya
The next step in the process is kiln firing. Based on lessons
learned from three Cambodian CWF producers, several small
kilns were built to ensure the precise control of firing
temperatures. The pots are manually loaded and the wood-
fuelled kilns are brought to a maximum temperature of
830 °C. During firing, the rice husk particles are completely
burnt off, thus creating miniscule pores in the body of the
pots. Digital pyrometers and pyrometric cones are used to
ensure the correct temperatures and to make any necessary
adjustments to the firing process. This key stage in the
manufacturing process determines the efficacy of the filter
elements. The increased porosity of the clay resulting from
the burnt off material determines the water flow rate and the
effectiveness of bacteria removal.
Mr. Wijeerathna adds finishing touches