From childhood we are being taught to Save Tap Water… but nobody has taught us in school how to save rain water. Nothing has been done to save rain water when it should have been the other way around. The ability to save tap water pales in comparison the sheer quantity of rainwater that is wasted into the sea through storm drain pipes. The ratio if there was any would be in the ratio of (1:23) 1 liter of tap water USED every day we have ignored 23 liters of rain water EVERY DAY.
The truth is India gets so much of rain… (whenever it rains)… that we no longer care to save rain water. So it just flows into the sea. Then there are periods of acute water shortage… this is also true in India’s Cherapunji which receives the highest rainfall in the WORLD.
We have in fact forgotten how to build step tanks in proportion to the population growth. Just like we forgot the principles of farming by 200 yrs of British rule we have also forgotten the importance our forefathers gave for ponds and water harvesting features. In farms people are covering and filling ponds for better agriculture output.
So how much rain water can we collect with a 1,000 sqft (3BHK) house roof in Mumbai? The answer is 192,780Lts per day. Or 1773, 50,200 Liters in 3 months of rain. (17 million ltrs or 1.7 Crore ltrs of rain in 3 months). How did we arrive at this figure?
As per the rain water calculation: (http://www.rainbarrelguide.com/how-much-water-can-you-collect-in-rain-barrels-during-a-rainfall/)
As per Wiki for Mumbai the average annual precipitation is 2,167 mm or 85 inches of rain https://en.wikipedia.org/wiki/Mumbai
Since 1,000 sqft can save 600 gallons as per the above link if we get 85 inches of rain in one day we get about 600gallons x 85 inch = 51000Gallons of rain water DAILY.
Now 1 Gallon = 3.78 ltrs so now we convert it into ltrs:
51,000Gallons x 3.78 = 192,780 Ltrs Daily!!!
In 3months of monsoon we get about 90 days x 192,780 = 1,73,50,200 Ltrs
Now if we divide the total amount of rain water collected in the year by 365 days we get 17350200/365 = 47,534 Ltrs per day!!!
Most people get about 2,000 ltrs of tap water for daily use in their house ceiling tank. Now if you waste your complete tap water daily you can waste only a maximum of 2,000ltrs daily while at the very same time you waste 47,534 ltrs (1,73,50,200/365) of rain water daily. This is a ratio of about 2: 47 or 1:23.
But are not our city buildings are committed to saving water by holding them in Cement Tanks & Sintex water tanks in the basement of the buildings. NO this is not water harvesting this is water storing and do not refill the groundwater. The capacity of any and all manmade tanks are limited and just a fraction of the size of chambers that nature has made in the belly of the earth… that too not far from the surface. The man made tanks cannot create rivers or increase water table.
Lack of Water Harvesting into Ground leads to Flooding.
On one hand wells and tubewells are running dry on other hands water is flooding the topsoil. So why is no rain water being channeled into wells and borewells to store water and refill the ground water table. These wells are actually openings to huge underground tanks which nature has prepared over the years.
What happens when you don’t do not store water underground? The Earth punishes you for being foolish!
The unsaved rain water starts flooding the streets, goes into the gutters and drainage pipes, sewage drainage systems, storm drain pipe lines and when 1 million homes let this water waste you can multiply 47,534 ltrs x million. This will create flood… massive flood especially if the tide is high and the storm drain pipes cannot empty the water into the sea.
Previously earthworms and dung beetle were taking away a lot of pressure and creating their own tunnels for the water to flood and refill the groundwater but now with the advent of chemical fertilizer and pesticide and concrete/tar roads the water do not enter the earth but flows from the top into surface water drains.
So next time somebody tells you to save tap water… ask them if they are saving rain water?