29 May 2004	Saturday	09 Rabi-us-Saani 1425

KARACHI, May 28: About 240 million gallons (43 per cent) out of the total 550 mg potable water, supplied to Karachi daily, is unfiltered, said KWSB sources.

It was learnt that the Karachi Water and Sewerage Board, which received water from three sources - Indus River, Hub Dam and Dumlottee wells - was unable to filter the entire quantity before throwing it into its distributaries, as it lacked the required facilities.

There was no filtration system for Dumlottee well water, as according to KWSB officials, it did not need any such treatment in view of the fact that it was already filtered through underground sandy beds.

About 90 million gallons of Hub dam water, which came through a long open canal, was also not filtered before pumped into the system, as KWSB was still in the process of establishing a filter plant of 100 mgd capacity.

The Hub filter plant of 80 mgd capacity was likely to go into operation by the end of this year, added a source. However, for treating the Indus river water, which was catering to the needs of major parts of the city for long, the KWSB had five filter plants, which at present were collectively filtering about 310 mgd water, while the remaining 130 mg unfiltered water was again mixed with filtered water in the KWSB system.

At NEK (Old) 25 out 38 mg was filtered, while at NEK (K-2 project) the entire 100 mg water was filtered. The COD filter plant received 150 mg but filtered only 115 mg, Gharo plant received 26 mg and filtered only 20mg, and Pipri plant filtered 50 mg of the 110 mg received.

It was further learnt that KWSB was working for increasing the capacity of the Pipri plant and it was likely that an additional filtering facility of 50 mg would be available at the beginning of next year.

When contacted, the Deputy Managing Director (Technical Services) KWSB, Suleman Chandio said that filtration was last of the 3-4 processes observed by KWSB for purifying water, and any deficiency on this side should not be taken as any major problem.

He said that suspended solids of settled water were passed through filter media to trap it and, thereafter, crystal clear water was passed on to the water tank for onward pumping.

The unfiltered water went through the process of chemical and mechanical treatments as well, while on the other hand certain physical treatment was also applied at the consumer end, he added.

He informed that the Hub water, mostly meant for the areas of defunct district west, remained unmixed with filtered water, while the remaining unfiltered water in other parts of the city got mixed with filtered water and thus any possible turbidity and contamination coming along with the unfiltered water had the chance of being diluted.

Talking about the chemical treatment, the DMD said that chlorine was applied to the entire quantity of water being supplied to the city from all sources, ie Indus, Dumlottee wells and Hub dam.

Chlorination was so arranged that at least 0.2 ppm was traceable at the tail-end of the water supply system. Under the mechanical system, water was passed through screeners where floating materials or solids were removed. Thereafter, it was passed through a chamber where silt or salt passed through screeners were trapped and removed.

After this, the available water was flown into chlorination tanks or clarified where the fine-sized solids were removed by giving them a 2- to 3-hour detention period, he elaborated.

To a question, he said that chlorine was used by KWSB in gaseous form, which ensured killing of pathogenic organism or coliform up to 99 per cent. He maintained that neither the Indus water nor the Hub water supplied in the KWSB system had turbidity of more than 3-5 ppm, and as such that water was considered right in line with WHO standards.