‘Mumbai needs to recycle its grey water’

The water table across all Indian cities falls by an average of around 0.3% each year, rising up to 4% in some areas. The need to conserve water is not a new conversation but the will to implement effective solutions has always been an issue.

At an event organised by the Columbia Global Centre here, Dr. Rakesh Kumar, director of the National Environmental Engineering Research Institute, spoke about the potential for grey water recycling in a city like Mumbai and some of the hurdles in its wider implementation.

Grey water is the water that is used and discarded in daily functions like bathing and washing clothes as opposed to water that is dispensed to sewage from toilets is called black water. Dr. Kumar said the water that can be safely used for recycling is that which comes from washing machines and bathroom sinks. While in other countries water from kitchens is also used, Indian cooking has a higher component of grease and that might make it unsuitable.

Dr. Kumar said studies showed that grey water of this kind has only 1% of contaminants which can be easily removed. Recycling it, he said, was a far more efficient system of conserving water than rainwater harvesting — widely proposed as a solution in Mumbai.

“Unlike many other cities, Mumbai has a big number of rainy days and the issue becomes where to store the water since we have a problem storing our regular water supply,” he said. “People say that it should be diverted to the ground water supply but groundwater is not a bank where you can put something in then withdraw. In most of Mumbai the groundwater is saline at a not very deep level,” he said.

Grey water recycling, he explained, can save up to save 35-40% of water consumption within a residential building and is now a key part of the green ratings that is given for buildings in India. Dr. Kumar said India has the highest number of green rated buildings in the world. While many of them are given for new constructions where infrastructure can be put in place, older buildings can also be certified. He gave the example of HPCL colony in Chembur which was recently certified after installing water recycling infrastructure.

Problem of perception

“Mumbai gets some of the cleanest water that comes from dams that are far away. Why should this water be used in the construction industry?” he asked.

Dr. Kumar said that the major challenge in implementing grey water recycling is not the technology, which is relatively cost effective, but the perception that there is not enough space in Mumbai to put up the infrastructure. “We need about five to 10 examples of big projects to come up so we can show it can be done,’ he said.

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Printable version | Jan 25, 2022 11:31:38 PM |

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