Is rainwater harvesting the solution for your dry taps?
“If the wars of this century were fought over oil, the wars of the next century will be fought over water,” said former World Bank vice president, Ismail Serageldin. He has been proved correct much faster than anyone else would have thought.
The taps have started running dry this summer and in the much-populated Mumbai City and its neighbouring suburbs. Th
e question, which will now be put forth before the administration is how cover this deficit. At present the city faces a shortfall of about 1200 MLD this year and this figure is bound to rise with every new construction in this city. The city receives approximately 4300 MLD to quench the thirst of millions of Mumbaikars, but this isn't sufficient.
Many ecologist and geologiost have come up with the idea of water conservation. The state government has made rainwater-harvesting mandatory for all buildings that are being constructed on plots that are more than 1,000-sqaure metre in size. Even the Kerala Municipality had amended their rules to include rainwater-harvesting structures in new construction.
Rainwater harvesting is the best way to preserve water and reduce flooding in the city. Eminent geologist Dr. Amar Joshi believes that the main caused of the reduction in the ground water levels and flooding in the city is the concretization of many of compounds in societies which is preventing the rainwater from entering the soil thereby decreasing the ground water level. Groundwater for commercial and personal consumption is extracted in an unplanned and uncontrolled manner. This has resulted in hydrological imbalance and deterioration in water quality.
Huge amounts of rainwater goes down the drain and is untapped resulting in the waste of million of gallons of portable water. "Most of the water during the monsoon season is wasted and untapped thus flowing into the drains. During high tide, this water is denied entry in the sea by the gigantic waves thereby causing flooding within the city," said Dr. Joshi.
What is rainwater harvesting (RWH) and how does it work?
Rain Water Harvesting is merely “putting back rain water into the soil, where it will be stored in underground reservoirs and fracture systems, so that we can draw it whenever we need it.”
A rainwater har
vesting system comprises of various stages - transporting rainwater through pipes or drains, filtration, and storage in tanks for reuse or recharge. The water the falls on the roofs and the ground surface is diverted to the catchments with the help of pipes which are then rooted to the well beneath the earth's surface. Gutters can also be built which will divert the water to the storage tank, which is then transferred to the well below. This increases the ground water level and reduced the salinity of the water. As and when the water is required, water can be lifted for use through the boring machines.
The Cost Factor
In order to install a rainwater harvesting system in your society of approximately fifty members, the cost for such installation would hover between Rs. 2 – 2.5 lakhs depending on the catchment area. Presently, the BMC charges around Rs. 3.50 per 1000 litres of water for the societies and Rs. 25 per thousand litres for industries. However, the break-even period for industries is much less for big industries as compared to the societies. It would take a society around 4-5 years to break even the invested amounts.
Dr. Amar Joshi believes that once this system is installed in your backyard, one does not need to worry for rest of their life. Every year, Mumbai receives approximately a hundred days of heavy rainfall. Hence if a society's terrace area is around 500-sq.m and open area (compound and garden) is around 1000 sq.m., rainfall that can be tapped during this period with the help of water harvesting is around 15,00,000 -20,00,000 liters per monsoon season. Many places in Mumbai have gone ahead with the tapping of rainwater. The residence of the mayor of Mumbai has the facility of rainwater harvesting. The total water which is tapped at the mayor residence every year is at a staggering 1,68,24,000 litres.
How can rain water help improve the lives of Mumbaikars?
With the help of this system, Mumbaikars can heave a sigh of relief resulting in a decrease in water bills and one can enjoy uninterrupted supply of water at a very low cost. Many places in Mumbai such as IIT, Municipal Corporation building, Raj Bhavan, BARC, VJTI College, Bhavan's College and St. Stanislaus School have successfully reaped benefits from using nature's priceless gift to mankind.