Before it is supplied to residents of Rawalpindi city and cantonment, and the capital water that accumulates in Rawal Dam from streams from Murree and nearby hills is processed by engineers and workers at a filtration plant to make it safe for human consumption.

At the Rawal Lake Filtration Plant, unfiltered water goes through a long process that involves screening, aeration, coagulation, flocculation, sedimentation, filtration, disinfection or chlorination and lime dosing before it is supplied to locals.

First, dam water runs through a canal on Chak Shahzad Road, where large particles such as tree branches, leaves, clothing, plastic bags and dead animals are removed. Then, to remove taste or odour from the incoming ‘raw’ water, it is aerated. Next, alum is added and mixed with the water to remove suspended particles in the form of turbidity.

During sedimentation, clear water is collected from the surface and settled material, in the form of sludge, is removed from the sedimentation tank with the help of sludge valves and rotating wipers.

The filtration process then begins. Suspended non-settleable solids are removed, and the sand is backwashed when it becomes clogged or when the turbidity of the filtered water gets too high. Sand is then fluidised and particles are flushed from the sand. The dirty, backwashed water is pumped into a settling pond – backwashing can consume between 1pc and 5pc of the plant’s production.

The water is then transported to a tank, where it is disinfected through chlorination and lime dosing, before it is ready to be transported through the water lines.

Water and Sanitation Agency (Wasa) Managing Director Raja Shaukat Mehmood told Dawn: “Raw drinking water quality in Rawal Lake has been deteriorating due to rapid urbanisation in the catchment areas and the raw sewage disposal of Bhara Kahu, Bari Imam, Quaid-i-Azam University, Chattar Park, Lake View Park, Rawal Dam Park and the adjoining housing societies through the Korang River and its tributaries.”

The construction of the Murree Expressway has also affected Rawal Lake, he said, causing excessive sediment transportation to the lake and virtually turning it into an oxidation pond. Mr Mehmood said: “It is not an easy job to provide potable water to the residents, and the polluted water of the Rawal Lake is purified through a long process.”

He said the filtration plant was upgraded by Wasa at a cost of Rs200 million. “The major scope of the work includes construction of a pre-sedimentation tank, pipe work from intake to the sedimentation tank and also flash mixture and up-gradation electrical and mechanical work of the Rawal Lake Filtration Plant,” he said.

He added that the process of turning raw water into potable water is monitored by the Water Quality Analysis Laboratory, where water samples are tested from the first step to the last step of the chlorination process. Wasa also checks the quality of water supplied to consumers, he said.

Colour, taste, odour, turbidity and chlorine coliform bacteria are the parameters of water quality, he said.

Mr Mehmood admitted that, while water is treated before it is supplied to consumers, some problems do occur in the narrow city streets, where water lines are punctured and mixed with sewage. He said the provincial government has launched a project to replace old and rusty water lines.

Published in Dawn, July 2nd, 2017