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Emergency treatment of Drinking Water at point-of-use

Charcoal filters

Charcoal can be quite effective at removing some tastes, odours, and colour. Ordinary charcoal available locally could be used, but activated carbon is more effective, though rather expensive. An example of such a filter is the Unicef upflow sand filter, illustrated in Figure 5. However, if the charcoal is not regularly renewed or if the filter is left unused for some time, it can become the breeding ground for harmful bacteria.

Ceramic filters

Water may be purified by allowing it to pass through a ceramic filter element. These are sometimes called candles. In this process, suspended particles are mechanically filtered from the water. The filtered water must be boiled or otherwise disinfected. Some filters are impregnated with silver which acts as a disinfectant and kills bacteria, removing the need for boiling the water after filtration. Ceramic filters can be manufactured locally, but are also mass-produced. They can be costly but have a long storage life and so can be purchased and stored in preparation for future emergencies. The impurities held back by the candle surface need to be brushed off under running water, at regular intervals. In order to reduce frequent clogging, the inlet water should have a low turbidity. Figure 6 shows a variety of ceramic candles.


It is essential that drinking water be free of harmful organisms. Storage, sedimentation and filtration of water reduce the contents of harmful bacteria but none of them can guarantee the complete removal of germs. Disinfection is a treatment process that ensures drinking water is free from harmful organisms or pathogens. It is recommended that this be the final treatment stage, as many of the disinfection processes will be hampered by suspended solids and organic matter in the water. There are various methods of achieving disinfection at household level:

Disinfection by boiling – Boiling is a very effective though energy consuming method to destroy various pathogens such as viruses, spores, cysts and worm eggs. The water should be brought to a rolling boil for at least five minutes and preferably up to a period of twenty minutes. Apart from the high energy costs involved in boiling, the other disadvantage is the change in taste of water due to the release of air from the water. The taste can be improved by vigorously stirring the water, or shaking the water in a sealed container after it has cooled.

Disinfection using chlorine – Chlorine is a chemical most widely used for the disinfection of drinking water because of its ease of use, ability to measure its effectiveness, availability and relatively lower cost. When used correctly, chlorine will kill all viruses and bacteria, but some species of protozoa and helmithes are resistant. There are several different sources of chlorine for home use; in liquid, powder and tablet form. Chlorine is commonly available to households as liquid bleach (sodium hypo chlorite), usually with a chlorine concentration of 1%. Liquid bleach is sold in bottles or sachets and is available on a commercial basis.

Chlorine must be added in sufficient quantities to destroy all the germs but not so much as to affect the taste adversely. The chemicals should also have sufficient contact time with the pathogens (at least 30 minutes for chlorine). Deciding on the right quantity can be difficult, as substances in the water will react with the disinfectant at different rates. Furthermore, the strength of the disinfectant may decline with time depending on how it is stored. It is therefore recommended that in emergency situations, chlorine solutions be centrally dispensed to the users by qualified personnel. Displaced people should receive standard containers for collecting/storing water, as well as simple dropper tubes or syringes. Technical staff should provide the instructions for mixing the chlorine solution, at the point of dispensing.

Solar disinfection – Ultra-violent rays from the sun are used to inactivate and destroy pathogens present in water. Fill transparent plastic containers with water and expose them to full sunlight for about five hours (or two consecutive days under 100% cloudy sky). Disinfection occurs by a combination of radiation and thermal treatment. If a water temperature of least 50°C is achieved, an exposure period of one hour is sufficient. Solar disinfection requires clear water to be effective.

An enhanced example is the SODIS system, whereby half-blackened bottles are used to increase the heat gain, with the clear side of the bottle facing the sun, as shown above.

Other water treatment chemicals

A number of commercially produced chemicals have been developed to holistically treat water at household level in emergency situations. Studies have shown that some of these powders significantly remove pathogenic bacteria, viruses and parasites from water. They also enable the particles to flocculate together, so they then to sink to the bottom of the container. Commercially available sachets typically treat 10lt of water. The water should be allowed to stand for at least five minutes before it is strained. It should be allowed to stand for a further 30 minutes before it is used for human consumption.

World Health Organisation

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