THIS is apropos of the news item ‘Karachi may be getting polluted water from Indus’ (Sept 16). The report says, among others:

(a) 100 mgd of raw, untreated water from the Indus is mixed with treated water from the KWSB’s water treatment plants, and this mixed water is supplied to the city.

(b) The KWSB claims that this water is fit for consumption.

(c) The quantity of chlorine has also been increased to ensure that all sorts of bacteria and germs are eliminated.

There are 14 rivers in Asia and the Pacific, which have thermo-tolerant coliform (TC) levels ranging from 100 to 1,000 per 100 ml, and three rivers with TC levels of more than 100,000 per 100 ml.

On the other hand, according to WHO, drinking water guidelines (2008), the water meant for drinking must have zero TC per 100 ml.

Mixing with contaminated water, containing more than 100,000 coliforms per 100 ml, will not produce safe drinking water. This practice is unheard of in water engineering and is responsible for the massive complaints of poor drinking water quality and of waterborne and diarrhoeal diseases, in Karachi.

In Sindh, municipal and industrial wastewaters are discharged untreated in the receiving streams. The Indus is, therefore, serving unjustly as a recipient of wastewaters of all the towns in Sindh. Wastewaters contain wide-ranging pollutants -- coliforms, oxygen-demanding substances, pathogens, organic and inorganic compounds and chemicals and heavy metals.

Also, fertilisers, insecticides, etc., are frequently used in Sindh. During wet seasons, these agrochemicals drain down to the Indus.

Persistent organic pollutants in the environment bio-accumulate through the food web, and pose a risk of causing adverse effects on human health and environment.

They result from industrial applications and waste incinerators.

In case of industries, like thermal power plants, parameters like mercury and temperature are of major concern. At Jamshoro, where power plants are also located, presence of mercury in the Indus water has been reported. Sudden increase in surface water temperature by three degrees Celsius is harmful for marine organisms.

The required level of oxygen is usually not available, as the increased water temperature decreases the solubility of oxygen in water.

Conventional water treatment plants (rapid sand filters for major cities; and slow sand filters for rural towns), depending on the quality of raw water, design and operation of the plant, remove conventional pollutants only, to a varying degree.

Karachi water treatment plants (rapid sand filters) do not remove heavy metals and chemicals. These are removed by tertiary or advanced water treatment.

According to FAO and USAID fact-sheets, floods have caused death of 1,800 human beings, 1.2 million animals, six million poultry and have destroyed two million houses. Houses in rural areas store, among others, the pesticides. All these deaths are decaying in river water, causing pollution.

This is enough to convince even a layperson that in order to produce safe drinking water, the Indus water needs appropriate treatment, before it is conveyed in Karachi’s water distribution system to citizens.

Potential benefit of chlorine becomes effective only when water turbidity is less than five ntu, even if enhanced dosage of chlorine is used. Turbidity of the Indus waters is 100 ntu and above. In addition, residual chlorine in water in excess of four mg/l will cause eye and nose irritation, chest congestion and stomach discomfort.

According to the UN’s General Comment No. 15 (2002), “The human right to water entitles everyone to sufficient, safe, acceptable, physically accessible and affordable water for personal and domestic uses.”

AN EXPERT Karachi