Chlorine not enough to purify water, says NED expert

Residents of Karachi have complained of non-chlorinated and reeky water over the last week.

KARACHI: That foul smell is not the trash in your house or the gutter outside - it is the smell of water in your taps. Residents of New Karachi, North Karachi, Surjani Town, Nazimabad and adjoining areas have complained of non-chlorinated and reeky water over the last week.

“Our water smells and we have no idea what is wrong,” says Junaid Rajput, a resident of Nazimabad. “We have to smell the water before letting it into the tank and I advise others to do the same.”

A Karachi Water and Sewerage Board (KWSB) engineer blames the utility for not adding chlorine to the water regularly. Not only is water supplied without necessary chlorination but alumen (a specific chemical compound of hydrated potassium aluminium sulfate), lime and other minerals to remove fatty contents are also not added, he claims. The lardaceous substances remain untreated and hence supplied.

Meanwhile, NED University’s architecture and planning department chairman Dr Noman Ahmed, also the author of a book on ‘Water Supply in Karachi’ (OUP), said chlorine cannot do enough to ensure a clean supply. “If the water smells, it most probably has some sewage mixed,” he tells The Express Tribune. Water and sewage pipelines in ‘remote areas’ such as North Karachi and Surjani are in the trench and the lines are laid close to each other. So any leakage - which is most likely to occur as pipelines are not periodically repaired - can result in mixing of sewage in the supply.

“The first sign of this happening is the smell,” says Dr Ahmed. “The mixing of impurities is a rampant occurrence as some pipelines are over four decades old.”

Chlorination seems like an economic and viable solution to the problem and KWSB chief engineer of the electrical and mechanical section Zaheer Abbas Zaidi assures that the process has not been interrupted. The ratio of chlorine to water is 1,000 kilogrammes to 100 million gallons of water every 24 hours, he informs.

But Dr Ahmed says chlorine cannot do enough to ensure a clean supply. “Chlorination only takes place when water enters Karachi city, that is, the areas of bulk water supply like the Gharo, Pipri and North-East Karachi pumping stations.” After that, the water has to travel long distances in broken or damaged pipelines, some laden with “inorganic harmful elements”.

Also in these areas, water can start smelling foul because the tanks underground or on rooftops are not cleaned frequently and residue and sediment collect at the bottom and in other storage utensils. According to a study titled “A Low-Cost Intervention for Cleaner Drinking Water in Karachi, Pakistan” published in International Journal of Infectious Diseases, June 2001, Vol 5, issue 3, even after chemical intervention, 99.8 per cent of the purifying chemical decreased in the stored water after some time. Fifty storage vessels were collected and purified by chemicals for the study and the vessels were collected by the experts after 10 weeks. It was found that even though water chlorination had markedly improved water quality, vessels that were not cleaned regularly and exposed to sunlight, ultraviolet light stabilisers and an unclean environment, had impure water.

According to Dr Ahmed, the only way to prevent impurities from mixing is by periodical repairs and maintenance.

Published in The Express Tribune, February 3^rd,  2011.