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Technology: Rainwater Harvesting - Part II

Ram Krishnan
02/05/2006

Rainwater Harvesting (RWH)
Need of the hour – in India (and many parts of the world)

“No water, No life”

What is Rainwater harvesting?

All forms of water anywhere in the world starts as rainwater. The total amount of drinking water in the world is about 1% of the total water mass.

There are 2 essential methods of collecting rainwater in a large urban metropolitan area. 

(1) Collect the roof water
(2) Collect the water on the sides of the building, trap it at the gate and charge it to the ground.

The following links will explain these methods.
      
A PVC pipe brings the water collected from the roof, pass thru a filter and collected into a sump    All the water rushing to the street is intercepted at the gate, using a trap. It is then filtered, piped to the sump or a baby well.

For a single dwelling house in Chennai, it would cost about Rs 6,000 to install. Most of the RWH components already exist. The typical house will have an existing sump designed to get and store municipal supply water. It will also have an electric motor to pump this water from the sump to an overhead storage tank on the rooftop and distribute water through existing plumbing. The only addition to this existing setup is the PVC pipes to collect the roof water during a rain,  filter it through a brick-sand filter and put the water into the sump. Excess water from the sump during the rain could be put into an existing well, or a baby well or a percolation pit based on the type of location.

For an apartment building (flat complex) with 25 tenants, a similar RWH design will cost about Rs 60,000. 

University (IIT) Hostels

There are 12 boys’ hostels in IIT Madras all named after India's rivers. Each hostel has around 300 students. With a daily demand per student of 45 litres, all the 12 hostels need 48,600,000 litres of water per year (300 usage days in a year). Prior to RWH, the water needs were met with 2 water tankers (12,000 litres per tanker) everyday for each hostel at a cost of about Rs 900 per tanker. Annual cost of purchased water is Rs 36,45,000. RWH installation at each hostel cost about Rs 3 lakhs for a total of Rs 36 lakhs. Water from the 12 hostels is diverted into 4 existing large agricultural wells - 40 feet diameter and 40 feet depth.  After RWH installation, we have met about 40-50% of the drinking water requirements. Additional wells can help meet 100% of the water requirements.

More about IIT Madras RWH pilot project
http://akash-ganga-rwh.com/RWH/IITM-RWH.html
     
Rainwater falling on the roofs of 12 hostels is collected and charged into nearby wells.    These wells (40 ft diameter and 40 ft deep) collect the rainwater and charge the underground for later use.

Recharging Bore Wells

People in urban and rural areas know how to get water by installing a borewell. Depending on the depth of the borewell - 100 feet to 600 feet-, a borewell will cost between Rs 0.5 lakh to Rs 2.0 lakh. The borewell unit consists of a deep pipe 3" diameter, an electric motor, a filter and a tap to deliver water. It is possible that when you drill a borewell at a given spot, you may not get water. If you try again 100-200 feet away, you may get water. The underground water is held in different pockets at different depths. Underground water is not one big connected lake. EVERY borewell will go dry once the water available in the vicinity of the borewell has been sucked up.

We must recharge an existing bore well, if we hope to continue getting water from the borewell. Water collected through rainwater harvesting can be recharged using a percolation pit located few feet away from a borewell. Combination percolation pits incorporated into the borewell unit designs are also available. We must think of every dried up borewell as a potential rainwater recharge unit.

Rural

The population of a village is around 1000 families. There are no pavements and parking lots blocking the natural water charging process in a village. The problem in a village is not as acute as in the city. But the village may only get a few inches of rain across 3 to 6 months of hot and dry weather. In certain parts of India like Karnataka and Uttar Pradesh with adequate rainfall, you can find ground water at depths of 10-20 feet. At the other extreme in parts of Tamil Nadu and Andhra Pradesh, you may have to dig 600 feet to find water.

The simplest and most inexpensive method of collecting rainwater is to dig series of shallow, circular pits (6 feet diameter and 1 foot deep) where rainwater is known to flow. Almost 80% of rainwater falling on flat rural lands is lost due to evaporation and runoff.

Three other forms of RWH can be recommended for rural areas.

(1) Build more community wells
(2) Build small check dams on small rivers and streams
(3) Rejuvenate existing water bodies, called ‘johads’ in Rajasthan and ‘oorani’ in Tamil Nadu.
          
Community wells help collect and recharge water during the rainy season.    6 to 8 feet high check-dams across small rivers helps to catch rainwater and supply both drinking and agricultural needs    Desilting and dredging a village drinking water pond provides year-long supply of water.

Benefits

When water returns to a village or a metro city, life itself returns.

If there is no water for agriculture, most villagers resort to dry agriculture (millet, sorgham etc) and animal husbandry (raising cattle). Once rainwater is collected in johads and agricultural ponds, they can raise 1 wet crop (rice, vegetables, musters seeds, potatoes etc) and sometimes even a second crop.

Summary

More information at:

Rainwater harvesting – An index of first information - India-centric
http://akash-ganga-rwh.com/RWH/WaterHarvesting.html

Invest in a Oorani
http://akash-ganga-rwh.com/Oorani/Invest-in-a-Oorani.html

Su Neer – E-Learning website for Rainwater Harvesting
http://adshare.adayana.net/suneer/index.htm

What you can do?

Join a Yahoo Group – “Akash Ganga Chennai” by sending an email to:
akashgangachennai-subscribe@yahoogroups.com

Install RWH in your house

Provide funds to assist your parents / relatives to install RWH in their premises.
Teach others about the benefits of RWH and urge them to install it.

RWH is easy and inexpensive. Just do it. 
Because - "no water, no life"

To contact Ram Krishan please send him an email at rkrishnan46@yahoo.com.

(RAM KRISHNAN an engineering graduate from IIT Madras, who has lived and worked in St.Paul Minnesota for over 30 years. He is currently Vice President of a Canadian software company called Descartes located in Waterloo Ontario. Few years ago, when the IIT Madras campus was partially closed due to shortage of drinking water, he learnt more about the problem, and about Rainwater Harvesting as a low-cost way for every citizen to help solve it. Ram Krishnan started a group consisting of about 10 local RWH experts to promote and encourage Chennai citizens to install RWH. He is currently the United States coordinator of the Akash Ganga project who also helped build the rain center. )

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Rainwater falling on the roofs of 12 hostels is collected and charged into nearby wells.


These wells (40 ft diameter and 40 ft deep) collect the rainwater and charge the underground for later use.


Community wells help collect and recharge water during the rainy season.


6 to 8 feet high check-dams across small rivers helps to catch rainwater and supply both drinking and agricultural needs.


Desilting and dredging a village drinking water pond provides year-long supply of water.

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