The Big H2O Conundrum

6 min readJun 14, 2018

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Rain water if harvested in Nagaland can meet about 61% of the water requirement for a family of 5.

It is a Sunday afternoon and Azo is slouched in his cushioned sofa flicking through the channels on his ultra HD LCD TV.

IPL. Click. More IPL. Click. Boring Parliament session. Click.

“Why can’t I find something worthy to watch among the 500+ plus channels I pay for?”

He mumbles in frustration.

“These Dish TV companies are a sca…O wait this is interesting.”

DD NEWS.

The anchor in her early thirties motions to the guest of her show to continue whatever he was speaking on. The banner below the screen read:

Bengaluru Scientist Hasn’t Paid Water Bill in 23 Years!

What seemed to a click baiting interview title by DD News turned out to be a very insightful one-to-one interview with A.R. Shivakumar or Bangalore’s Rain Man who has indeed not paid the water bill for the past 23 years because he doesn’t need to. His daily water demand is met through meticulous harvesting of rain water as he collects and treats the rain water for his day to day uses and also to recharge the ground water table below his plot.

A R Shivakumar ( Photo Credit: The Better India)

This got Azo thinking as he picks up the local newspaper and skims through the recent advertisements for bore wells in Kohima.

If this man can be do something like that in Bengaluru with an average annual rainfall of 859 mm and gross rainfall days of 60–70 per year, then imagine the prospects of implementing this in Nagaland which is one of the wettest states in India receiving an average annual rainfall of 1800–2500 mm stretching from May right up to September.

So what really is this Rain Water Harvesting (RWH)?

Rain Water Harvesting (RWH) is the technique of collection and storage of rainwater rather than allowing it to run off. The most common method of RWH is rooftop harvesting where the roof of the house is used to intercept the flow of rainwater. This harvested water can be used as drinking water after treatment, long term storage or to recharge the groundwater

Benefits of Harvesting Rainwater

· Naturally pure

· Naturally soft (no dissolved minerals)

· Sustainable

· Free of chlorine and its byproducts

· Free of pesticides and other man-made contaminants

· Reduces run-off and erosion

Economic feasibility

The rain water yield is calculated by the formula:

Rain water yield (Litres per Year) =Roof area (sq. m) * Annual rainfall (mm) * Run-off coefficient * Filter efficiency

Roof area= Length * Width of roof.

Run-off coefficient: Loss due to slope of roof, velocity of wind, evaporation.

Filter efficiency: The efficiency with which the filter arrest impurities and even kill pathogens (in case of slow sand filter).

Example: Consider a building complex of roof area of 10*10 sq. metres in Kohima (annual rainfall = 1863 mm).

Run-off coefficient = 0.9 (GI Sheets roof) and Filter Efficiency = 90% (Slow Sand Filter).

Then Rain water yield = (10*10)* (1863)* (0.9) * (0.9) = 1,50,903 Litres per Year.

The average consumption of water in India = 135 Litres per Day (According to United Nations Development Program).

Therefore the average annual water consumption for a family of 5:

(135)*(5)*(365) = 2,46,375 Litres per Year.

Which means rain water if harvested can meet about 61% of the water requirement for a family of 5.

The concept of rain water harvesting is not totally new to the people of Nagaland as exhibited by the people of Kikruma village who has been practicing an ingenious method of impounding water called ‘Zabo’ for catching rain water before it runoffs the hilly terrains of the mountains

Most of the houses are fitted with drainage systems to drain the rain water off but this water remains practically unusable for anything other than flushing or laundry. The rain water collected has high turbidity, blackish colour and contains potential pathogens due to roof contaminants such as bird excreta, dust, dirt and debris from the environment.

A very common solution to this would be providing a ‘First flush system’ which takes the first water from the roof and diverts it away from the storage tank so that it flushes the water from the roof contaminants before the water is diverted to the storage units. A T pipe fitting can be used as a first flush system where the first flush is carried out by sealing off the horizontal flow of water through the T-section for some time after the rain starts and after satisfactory flushing of the roof the vertical section of the T- pipe is closed off thereby allowing the rain water to be diverted to the storage or treatment units.

First flush pipe fitting( Photo Credit: www.harvesth2o.com)

The first flush system coupled with a ‘Slow Sand Filter’ can be employed for robust treatment of rain water which can remove the bacterial content present hitherto to a satisfactory 90–99%. Subsequent disinfection of the filtered water by using Chlorine can also be employed which not only kill potential pathogens that have seeped through the filtration process but also safeguard the water against future contamination.

Slow sand filter design (Photo Credit: www.sswm.info )

The recent news about the citizens of Shimla queuing up for days as the city’s water reserves officially went dry should be a grim reminder about the ground reality of the scarcity of water and even more the need for utilizing and conserving available resources for the near future. According to Rajendra Singh a.k.a. India’s Waterman,

“More than 70% of the ground water in the country is currently ‘overdraft’ which means we have taken more water than the recharge”.

Shimla (Photo Credit: www.firstpost.com)

Excessive drilling of bore wells has led to exploitation of groundwater at higher rates than the rate of water recharge and caused depletion of the groundwater levels. To monitor this many states like Karnataka and Kerala have come up with laws & a statutory authority to regulate and keep tabs on the groundwater utilization. Some states have implemented groundwater legislation acts which prevent drilling of bore wells without the permission of Government Bodies in water scarce regions.

The recent announcement by the honourable government P.B. Acharya for 50% subsidy for setting up 1000 litres tank within Kohima is a positive step forward and there is a dire need for more of such government backed initiatives that invites not only individual stakeholders but communities (colonies or wards) as a whole- an incentivized scheme perhaps in this direction that calls for concerted participation and management of rain water harvesting assets from every household in a community.