COMMENT: Turbid water renders chlorination useless

Published June 17, 2024
A chlorine cylinder is moved into place at a KWSC pumping station.—Fahim Siddiqi / White Star
A chlorine cylinder is moved into place at a KWSC pumping station.—Fahim Siddiqi / White Star

On April 12, 2024, a 14-year-old boy and six-year-old girl died on the first day of Eid after remaining ill with acute diarrhoea for some days. They were residents of Nazimabad. The water suppled to their locality by the water board was visibly contaminated and stinking, and had worms that could be seen with the naked eye.

Worms in water is the worst type of drinking water pollution in Karachi.

A team of the health department and water board reached the spot, and distributed chlorine tablets among the residents, most of them illiterate.

Chlorination of drinking water is not that simple. A number of parameters impact the chlorination process.

Chlorination will not be effective if the turbidity of water is more than 5ntu (nephelometric turbidity units). This is because the suspended particles protect microorganisms, which embed themselves within the particles, to escape the disinfection.

Drinking water in Karachi is turbid (turbidity greater than 10 ntu). It is useless to waste chlorine on such waters. Turbidity must be brought to 1ntu, for chlorination to be effective.

Chlorination is impacted by the pH value of water. A measure of the degree of the acidity or the alkalinity of a solution. The optimum range of pH for chlorine disinfection is between 6.5 and 7.5. The effectiveness of chlorine disinfection reduces by a factor of between three and six, when pH increases from six to nine. Chlorine disinfection is poor when the pH is above nine.

Temperature of water also impacts disinfection efficiency. Temperatures above 20°C (Celsius) are suitable for disinfection. When temperature drops below 20°C, the disinfection efficiency reduces.

Disinfection efficiency is significantly impacted by the contact time. Contact time is defined as the period available for the interaction between the disinfectant and constituents in the water. The minimum contact time for chlorination should be 30 minutes at 20°C, to ensure effective disinfection. In case of Karachi, this means that there must be the contact time of 30 minutes of chlorine with water, before the water reaches “the first consumer”. If the temperature drops below 20°C, the contact time should be increased. Contact time increases from 30 to 60 minutes, if the temperature drops from 20°C to 10°C.

The generally accepted value of residual chlorine of 0.5 mg/L (milligrams per litre) is required to be maintained in the distribution system up to the last customer.

The World Health Organ­isation (2008) gives the guideline value of residual chlorine as: “For effective disinfection, there should be a residual concentration of free chlorine of 0.5 mg/L, after at least 30 minutes contact time at pH less than 8.0”.

Chlorine has also a dark side. Chlorine reacts with naturally occurring organic matter (eg decaying leaves and vegetation) to form trihalomethanes.

The forms of trihalomethanes commonly found in drinking water are chloroform, bromodichloromethane, dibromochloromethane and bromoform. All these four form are carcinogenic.

The performance of Karachi water utility is not up to the mark. The report of Commission of Inquiry of Mr Justice Muhammad Iqbal Kalhoro of Feb 25, 2017 has this to say on the performance of Karachi and Sewerage Board (KWSB) — which has now become Karachi Water and Sewerage Corporation (KWSC) —: “These are 07 Filter Plants in Karachi, out of which 06, KW&SB claimed, are functional. The undersigned during the inspection of these facilities, however, did not find any evidence supporting such claim. There was no trace of 24 hours chlorination with residual doze to kill bacteria. Neither the filtration beds were working properly, nor the Clarifiers were operational. At the time of visit some arrangements were made to show chlorination of water was going on but it was obvious that the whole preparation was contrived only for the occasion.

“The chlorination tanks seemed rusty and appeared to be in disuse for a long time. No record of purchasing chlorination was produced by KW&SB officials at any of the Filter Plants, nor was any confirmed figure of quantity of chlorination being mixed through chlorinators presented. At NEK Filter Plant, the chlorination tank was found leaking to such a degree that no one could stand there for a minute. None of the officials of KW&SB including DMD could explain how with such leaked tanks the procedure of chlorinating water was being accomplished.

“The chlorinators although were shown to be functioning at COD Filter Plant, but no record of monitoring due dose of chlorination of water or any such statistics was produced nor was it informed if there was any such mechanism in place. At Manghopir Filter Plant one out of two chlorinators was found non-functional. The official in-charge there admitted that it was in disuse for a long time and in the facility attention mainly on the quantity of water and not the quality was being paid. He admitted that chlorination was not the priority of KW&SB.

“The inspection of these Filter Plants demonstrated clearly that the water was merely being routed through them with no chlorination and inadequate filtration. As no creditable evidence of complete doze of chlorination of water was traced in any of the Filter Plants, nor were such statistics produced, it is safe to say that water full of all contamination that includes turbidity, color, odor & taste, TDS, Hardness, Calcium, Sodium, Potassium, Chloride, Sulfate, Fluoride, Nitrate and Iron etc. in high volume is being supplied to the people of Karachi. This conclusion has been further confirmed by the result of test report of water-samples submitted by PCRWR.

“Overall data shows that out of 84 samples 67(80%) were found unsafe for drinking purpose, while only 17(20%) samples were found fit for human consumption for analyzed parameters under prescribed standards.”

On water shortages in Karachi, the inquiry report says: “The revelation about illegal hydrants is also strengthened by the statement of Muhammad Hassan Bakshi, Acting Chairman, Association of Builders and Developers Pakistan, who states that price of 1000 gallons of water through pipelines is Rs.245/- only, whereas through tanker it costs Rs.4000/- to 5000/-. A deliberate situation of shortage of water has been created by KW&SB to earn millions of rupees illegally.”

Need for reforms in KWSC

There is a vast scope of reforms in the KWSC. The first thing the service provider has to do is to realise that people have right to safe water and sanitation.

The United Nations General Assembly Resolution A/RES/64/292 adopted by the General Assembly on 28 July 2010, “recognizes the right to safe and clean drinking water and sanitation as a human right that is essential for the full enjoyment of life and all human rights.”

The Human Rights Council’s Resolution A/HRC/RES/15/9 reaffirming all previous resolutions of the council on human rights and access to safe drinking water and sanitation.

The 64th World Health Assembly of the World Health organisation, vide Resolution A64/24 of 14 April 2011, lays down the strategies for the safe management of drinking-water for human consumption.

The water utility should work for the poor people in Karachi by providing them safe water supply round-the-clock. Water utilities in Uganda, Cambodia and the Philippines all work for the poor people.

A paper by Franceys and Gerlach (2008) argue that “Improving services to the poor requires a good enough utility that has been facilitated not only to move towards sustainability through viable tariffs and better management of water losses but also to be creative in recognizing presently indirectly served low-income consumers as potential revenue generating customers.”

Important components of reforms, specific for Karachi, include reduce unaccounted-for water, provide metered water supply, professionalise the operation and management of piped water systems, adopt state-of-the-art technology to address water quality issues, meet Sustainable Development Goal (SDG) six by increasing water access, and prepare strategies for adaptation to the climate change challenges (floods, drought, extreme temperatures, source water quality, and sea-level rise).

The writer earned his master’s degree in water and wastewater engineering from the Asian Institute of Technology, Bangkok, in 1975.

Published in Dawn, June 17th, 2024

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