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Harriette Purchas gravatar image
RedR TSS

Chlorination is a very effective method of disinfection for drinking water, under the right conditions.
The main advantages for chlorination of surface water for drinking are:

• It destroys most pathogens that are commonly found in surface water. Chlorination of drinking water, together with safe water storage, can make a significant reduction to the incidence of diarrhoeal diseases.

• It can be a cost effective method of disinfection using products that are readily available locally such as household bleach; and

• It can be relatively easy to apply.

Some disadvantages of household level chlorination are:

• Some pathogens found in surface water – such as Giardia Duodenalis and Cryptosporidium Parvum - are highly resistant to normal levels of chlorination. However, with pre-treatment such as filtration these can be removed.

• The water to be treated should be relatively free of organic content, such as silt and leaf mould. The quality of surface water can be very variable, particularly after heavy rainfall, requiring varying doses of chorine to be effective. The householder will require some training to be able to calculate and apply correct dosing, which can be difficult. Too little chlorine will result in some pathogens remaining in the water. Too much chlorine will result in bad taste of the water.

• A supply of chlorination product must be readily available.

• Chlorination products such as household bleach can be dangerous if ingested without dilution and should be stored safely away from children.

It must be noted that safe storage of all drinking water is essential to prevent recontamination after disinfection.

There is a lot of good documentation on this subject and I have listed a few here:
A WELL factsheet on chlorination is available: http://www.lboro.ac.uk/well/resources/fact-sheets/fact-sheets-htm/chlorination.htm

UNICEF have written a good report on Promotion of Household Water Treatment and Safe Storage: http://www.unicef.org/wash/files/Scaling_up_HWTS_Jan_25th_with_comments.pdf

WHO have also produced an excellent Technical Note on measuring chlorine levels in water supplies, designed for use in emergencies but also applicable otherwise: http://wedc.lboro.ac.uk/resources/who_notes/WHO_TNE_11_Measuring_chlorine_levels_in_water_supplies.pdf