Slow sand filtration water treatment plants
Practical Action
Special emphasis was placed on the use of pre-filters for high-turbidity water, particularly
during the rainy season, as this improves the quality of the water entering the filter so that it
will work effectively.
DESIGN
Before embarking on a treated water supply project, it is essential to evaluate and define the
level of organisation in the community. If it is insufficient or non-existent then the operation
and maintenance of the system will most likely be neglected and eventually abandoned.
The community must participate in every stage of the installation of the water supply service,
including the selection of the technical option, the construction and supervision of the works
and the management of the service.
In the design stage, the community must study the proposed solutions and decide upon the
best technical alternative and the most appropriate service. Consequently, they must be
aware of the costs of the system – including their own contribution to the construction and
the rates to be paid, the advantages and disadvantages of each alternative and their
operation and maintenance responsibilities (UNDP 1998).
The following factors must be borne in mind for a preliminary study to define possible water
treatment solutions:
Weather conditions: The temperature has a substantial influence on the performance
of water treatment systems and the intensity and duration of the rain influences the
quantity and quality of the source.
Watershed characteristics: Human and natural factors, such as discharges of
residual water or run-off from chemically treated farmland, can seriously affect the
quality of the water.
Quality of the water: A physical, chemical and bacteriological analysis of the water is
necessary in order to determine its quality and the level of treatment required.
Location of the plant: The land must be easily accessible, having a natural slope of
between 5 and 10% and having no exposure to natural hazards or to subterranean
water nearby. A written agreement with the owner must be signed.
Characteristics of the community: It is necessary to know the customs and beliefs
that could affect the acceptance of the system, the characteristics of existing
organisations, the availability of natural materials and human resources, and the level
of schooling.
Existence of water-related diseases.
5