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The grey area

Recycling grey water that is discharged by homes can solve water problems to a great extent. Photo: H. Vibhu   | Photo Credit: H. Vibhu

Citizens across the world are facing a water crisis. For example, six months ago, this newspaper reported that the groundwater level in Chennai fell by 0.5 meters to an average of 4.7 meters in just one year. Adding to these woes was the information that groundwater quality had also deteriorated with a 200 ppm increase in total dissolved solids (TDS).

Root causes?

Of all the fresh water in the world, only 3 per cent is found on the surface of the earth in the form of rivers and lakes. The rest is below the surface, in aquifers, also known as groundwater. Surface water and groundwater are fundamentally different. Water from a river can be recharged in 20 days through rainfall. However ground water is accumulated over a period of hundreds of years as the water percolates through several feet of topsoil, rocks etc. Therefore ground water is ancient water. To give an example, the Great Artesian Basin is an underground aquifer supplying water to Australia. In some parts, the water in this aquifer is nearly 2 million years old!

In India, 90 per cent of our drinking water comes from ground water. We are utilizing ground water at an alarming rate compared to the years it takes for that same water to be recharged by natural processes. This is why human intervention like rain-water harvesting is crucial to maintain groundwater levels. We must also remember that groundwater is easily contaminated by effluents from polluting industries and household waste. Since the water is deep under the surface, once contaminated it is very difficult to purify.

In this context, it is our civic duty to examine the waste water generated in our homes and implement simple solutions to recycle water.

Household waste water

In the last four articles we explored drinking water purification methods for the home in great detail. While safe drinking water is vitally important, it only forms a small part of a household’s water consumption. Bathing, laundry and flushing will account for anywhere between 60 to 70 per cent of the water consumed in an Indian home. Apart from drinking water and that used for cooking, all other water leaves the house as waste water through the sewage lines.

Household waste water falls into two broad categories – Grey Water (leftover from bathing, hand-washing, mopping floors) and Black Water (waste water that contains human waste including fecal matter). Waste water from laundry is tricky to classify. Laundry water is also the largest source of waste water in a home. Normal detergents used for laundry have high level of phosphates, which means that the water from a washing machine cannot be recycled without prior treatment or filtration. Water from the kitchen sink, after cleaning vessels also requires filtration before it can be recycled. For the purposes of our discussion, we can classify laundry and kitchen sink water as grey water.

Of all the fresh water a home receives, roughly 50 per cent leaves it as grey water. Grey water recycling offers a huge opportunity for responsible citizens to play their part in solving a global water problem. Even black water can be recycled although it requires several filtration steps to remove the waste. In Singapore the water crisis has reached such alarming levels that the government has set up a treatment plant to produce drinking water from recycled, treated sewage water (black water). Ironically some lab tests have reported that this recycled sewage water is cleaner and safer to drink than the usual fresh water source.

This series of articles will explore simple ways to conserve water around the home with a particular focus on grey water recycling.

The writer is an environmentalist and CEO of Krya, a company that deals in products for sustainable urban living.

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Printable version | Jan 26, 2021 6:07:28 AM |

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