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
Research in Ecudaor shows that in practice household chlorination is ineffective for many of the reasons listed as disadvantages in Harriette's answer:
- source water turbidity
- source water baseline contamination levels, and
- in-home contamination
Can you realistically expect (illiterate) rural householders to accurately measure "both source water and household conditions to determine appropriate chlorine levels"? How much will it cost to train and monitor communities to make household chlorination effective and sustainable?
Levy, K. et al, 2014. Household effectiveness vs. laboratory efficacy of point-of-use chlorination. Water research, DOI: 10.1016/j.watres.2014.01.037
McLaughlin, L.A. et al, 2009. An observational study on the effectiveness of point-of-use chlorination. Journal of environmental health, 71, 8, pp. 48-53. http://www.sph.umich.edu/scr/ecodess/news_docs/McLaughlin_etal2009.pdf
In addition to the problems controlling dosage as listed in the previous posting, many chlorine compounds degrade over time and so it is impossible to estimate the chlorine dose without testing. One approach that is widely practiced in emergency situations, such as epidemics and accommodating large displaced populations, is the use of chlorine tablets. Ones based on NaDCC (sodium dichloroisocyanurate) are approved for use in such situations by a number of organisations and they are available in a variety of doses to suit different quantities and qualities of water. They are also far more stable than hypochlorite compounds.
With close supervision and education this type of intervention is credited with having significant impact on disease transmission. However, for routine household use, it is dificult to see how this approach can be made sustainable.
You might also find this discussion useful in which NaDCC is contemplated as an alternative to point of use ultrafiltration:
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