Household water treatment systems
Practical Action
Alternative treatments include chlorine dioxide Cl2 or ozone O3.
UV Treatment
UV light can be used to kill pathogens in water if the water does not have a large quantity of
physical contamination which would block the light (i.e. have a high turbidity). UV light between
the wavelengths of 180-320 nm can inactivate protozoa, bacteria, yeasts, viruses, algae and
fungi. It can be done on a large or small scale. It does not remove chemical pollutants but it can
be used as a catalyst when using an ozone treatment.
At its most basic level Solar Disinfection (or SODIS) 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/.
MEDRIX have developed a small scale UV water treatment system.
USA Mailing Address:
MEDRIX
PO Box 178
Redmond, WA 98073
USA
Phone: (425) 485-5423
Fax: (425) 485-4972
E-mail: office@medrix.org
Website: http://www.medrix.org/water.html
Vietnam Office:
MEDRIX
10th Floor
Prime Business Center
Pacific Place Building
Ly Thuong Kiet Street
Hoan Kiem Dist.,
Hanoi, Vietnam
Distillation
Distillation can remove virtually all salt, nitrates, and heavy metal such as arsenic from water as
well as pathogens and other biological contaminants from water.
Distillation will remove chemicals but it may not be easy to sustain as it uses a lot of energy.
However, heat could be obtained from the sun. Solar distillation is a low cost but low volume
approach to treating water. Essentially water is evaporated by the sun and condenses on a cooler
surface from where it is collected. A common design of a solar still is shown below. A glass or
plastic plate is fixed on top of the still to increase the temperature in the still, and the bottom of
the still is lined with a black material such as bituminous paint, butyl rubber, epoxy enamel,
fibreglass painted black or aluminium painted black, to act as a heat absorber. It is also
important that the whole still is well-insulated to improve efficiency. The sides and base of the
still are typically brick or concrete. Moulding of stills from fibreglass was tried in Botswana.
This was more expensive than a brick still and more difficult to insulate sufficiently, but has the
advantage of the stills being transportable.
Figure 5: Schematic of a single-basin still. Illustration: Otto Ruskulis for Practical Action.
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