Household water treatment systems
Disinfection and Sterilisation
Chlorine is an oxidising agent. It is cheap, reliable and easy to add to the water supply but it
can produce a nasty taste. Chlorine will kill the algae that clean water in slow sand filters so
should only be used after filtering if used together. Chlorine should be added in quantities
that leave a residual amount of free chlorine in the water of 0.3mg/l after 30 minutes.
Solutions of chemicals containing free chlorine such as bleaching powder, chlorinated Lime,
sodium hypochlorite or HTH. Alternative treatments include chlorine dioxide Cl2 or ozone O3.
Ultraviolet (UV) Treatment
UV light can be used to kill pathogens in water if the water does not have a large quantity of
physical contaminants which would block the light. It can be done on a large or small scale.
At its most basic level SODIS or Solar Disinfection can be carried out by placing water in
transparent plastic bottles which are then left out in direct sunlight thus exposing the
pathogens’ to UV light which destroys them. See http://www.sodis.ch/.
Domestic scale bio-sand filters
Practical Action has used bio-sand
filters in Peru and in Bangladesh and
they have been promoted in many
other countries by other organisations.
The filters were first used in Haiti in
1999 and their usage is spreading
throughout the country as people
become more aware of their
effectiveness. The following
description is of the domestic scale
bio-sand filter used in Bangladesh.
This Bio-sand household filter is a
fairly recent innovation in Bangladesh,
but has undergone extensive testing at
the University of Calgary in Canada.
The filter is a small, household sized
adaptation of slow sand filters such
that they can be run intermittently.
Figure 2: Domestic water filer used in Peru. Photo:
The Bio-sand filter’s simple technology, its proven effectiveness and availability of production
materials are what make it a viable option for Bangladesh. In a country where education is
limited, people of all ages, including young children, are able to use the filter and understand
how it works.
The system has proven effective and has become one of the most widely distributed devices
for household water treatment in developing countries.
Figure 3: Bio-sand filter cross section.