The monsoons are a particularly favourable time for the spread of waterborne diseases. As streets get flooded and groundwater tables rise, they tend to contaminate open wells and bore wells alike. Even piped water supply lines which are empty can pick up contaminated water. There is no tolerance limit for the presence of bacteria in the form of either total coliform or faecal coliform in potable water as far as Indian standard for drinking water quality is considered.
For over a century chlorine has been used by engineers as a water disinfectant. A residual chlorine of 2 parts per million is considered the best way of disinfecting water. Four kinds of chlorine agents are used for water disinfection: chlorine gas, sodium hypochlorite, calcium hypochlorite, and chlorinated iso-cyanurates.
The good and bad of chlorine
While chlorine gas is extremely dangerous and requires specialised handling, the typical form of using chlorine in India is through bleaching powder which is calcium hypochlorite or sometimes liquid chlorine which is sodium hypochlorite. The available chlorine in bleaching powder varies between 25 and 60 per cent and for sodium hypochlorite between six and 12 per cent.
Chlorine kills bacteria by transforming itself into hypochlorous acid when dissolved in water. Chlorine works best when the water is slightly acidic i.e. when the pH of the water is between 5 to 7. It is best therefore to test the water from the borewell or in the sump and ensure that the pH meets this requirement before using bleaching powder or liquid chlorine for disinfection. While water supply utilities ensure a higher residual chlorine in water during the rains it is for the consumer to manage the disinfection of water if the source is private water tankers, borewells or open wells.
It is good to get sump water and borewell water checked in a lab for the presence of coliform bacteria. More and more borewells report the presence of either total coliforms or faecal coliforms even from depths of 600 ft. in Bangalore. If the borewell water is smelly this too may indicate the presence of bacteria.
Shock chlorination
For borewells, shock chlorination is recommended. A high dose of chlorinated water using bleaching powder thoroughly dissolved in two to five buckets of water is poured into the borewell.
Using a hose pipe more water is poured into the borewell so that the chlorine is thoroughly mixed into the water.
When the borewell water is pumped out it should smell of chlorine.
This should be allowed to act for about 24 hours. Water from the borewell should not be used during this time. Shock chlorination may be necessary a few times if the contamination continues or even continuous chlorination may become necessary for deep borewells.
The Japanese company Shikoku has come out with a very interesting set of products called Neo-chlor where the available chlorine can be as high as 90 per cent. The product too has a shelf life of two years, making it possible to use it for long after purchase.
A slow release granular form of powder is best for sumps while for borewells it may be possible to use a little amount of the powder form dissolved in water.
Products which are safe and easy to handle, which have a long shelf life, which do not cause scaling, and which are not harmful in accidental contact and handling and also products which come with detailed instructional manual for use are the necessity of the day in India where water quality is increasingly compromised with bacterial contamination. Customer education is paramount with a good reliable product.
Organo-chlorines are a negative externality which will need to be considered but for the moment the good impact of chlorine may be more apt for the Indian water sector. Using it wisely and carefully is the road to water wisdom.
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