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Rainwater harvesting
Contents:
1. Introduction
2. Objectives
3. What is rain water harvesting?
4. Necessity of rain water harvesting.
5. Methods of rain water harvesting.
6. Advantages of rain water harvesting.
7. Disadvantages of Rainwater Harvesting.
8. Conclusion.
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1.Introduction
• Rain water harvesting is an outcome of awareness among the
people regarding the water scarcity
• Reutilization of waste water.
• As rain water harvesting -neither energy-intensive nor labor-
intensive.
• It can be a cost-effective alternative to other water-accruing
methods.
• With the water table falling rapidly, & concrete surfaces and
landfill dumps taking the place of water bodies, RWH is the
most reliable solution for augmenting groundwater level to
attain self-sufficiency.
• This can be used for private and public buildings as well as for
many industrial areas.
• Beyond that rainwater harvesting plays an important role for the
rainwater management of housing estates.
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2.Objectives
• Increasing the availability of ground water during periods of
requirement.
• Preventing depletion of ground water reservoir in areas
of over exploitation.
• Decreasing menace of flood on local and regional scale.
• Reducing pressure on storm drains in urban areas.
• Enhancing the quality of environment.
• To reduce groundwater pollution.
• To reduce soils erosion.
• Supplement domestic water needs.
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3.What is rain water harvesting?
• It is the activity of direct collection of rain water
• The harvesting of rainwater simply involves the collection of
water from surfaces on which rain falls, and subsequently
storing this water for later use.
• Normally water is collected from the roofs of buildings and
stored in rainwater tanks.
• Water can also be collected in dams from rain falling on the
ground and producing runoff.
• Rain water can be stored for direct use or can be recharged into
the ground water aquifer.
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4.Necessity of rain water harvesting
• To conserve & augment the storage of ground water.
• To reduce water table depletion.
• To improve the quality of ground water.
• To arrest sea water intrusion in coastal areas.
• To avoid flood & water stagnation in urban areas.
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5.Methods of Rainwater Harvesting
Broadly there are two ways of harvesting rainwater.
(i) Surface runoff harvesting
(ii) Roof top rainwater harvesting
1. Surface runoff harvesting
• Rainwater that is not captured directly, used by agriculture, or
absorbed into the ground becomes surface water.
• Surface water harvesting includes all systems that collect and
conserve surface runoff after a rainstorm or in intermittent
streams, rivers, or wetlands for storage in open ponds and
reservoirs.
• This can provide water for direct household use, irrigation, and
livestock.
• Storing water in an aquifer conserves water better as it prevents
evaporation.
• In urban area rainwater flows away as surface runoff. This runoff
could be caught and used for recharging aquifers by adopting
appropriate methods.
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5.Methods of Rainwater Harvesting
2. Rooftop rainwater harvesting
• In rooftop harvesting, the roof becomes the catchments, and the
rainwater is collected from the roof of the house/building.
• It can either be stored in a tank or diverted to artificial recharge
system.
• This method is less expensive and very effective and if
implemented properly helps in augmenting the groundwater level
of the area.
Types of Rooftop rainwater harvesting
a) Storage of Direct Use
• In this method rainwater collected from the roof of the
building is diverted to a storage tank. The storage tank has
to be designed according to the water requirements, rainfall
and catchment availability.
• Each drainpipe should have mesh filter at mouth and first
flush device followed by filtration system before connecting
to the storage tank. It is advisable that each tank should have
excess water over flow system.
• Excess water could be diverted to recharge system. Water
from storage tank can be used for secondary purposes such
as washing and gardening etc. This is the most cost-
effective way of rainwater harvesting.
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5.Methods of Rainwater Harvesting
b) Recharging groundwater aquifers
Groundwater aquifers can be recharged by various kinds of
structures to ensure percolation of rainwater in the ground instead of
draining away from the surface. Commonly used recharging methods
are:
• Recharging of bore wells:
Rainwater collected from rooftop of the building is diverted
through drainpipes to settlement or filtration tank. After
settlement filtered water is diverted to bore wells to recharge
deep aquifers. Abandoned bore wells can also be used for
recharge.
• Recharging of dug wells:
Dug well can be used as recharge structure. Rainwater from the
rooftop is diverted to dug wells after passing it through filtration
bed. Cleaning and desalting of dug well should be done
regularly to enhance the recharge rate. The filtration method
suggested for bore well recharging could be used.
• Recharge pits:
Recharge pits are small pits of any shape rectangular, square or
circular, contracted with brick or stone masonry wall with weep
hole at regular intervals. Top of pit can be covered with
perforated covers. Bottom of pit should be filled with filter
media.
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5.Methods of Rainwater Harvesting
• Recharge Trenches:
Recharge trench in provided where upper impervious layer
of soil is shallow. It is a trench excavated on the ground and
refilled with porous media like pebbles, boulder or brickbats. it
is usually made for harvesting the surface runoff.
• Soakaways or Recharge Shafts:
Soak away or recharge shafts are provided where upper layer of
soil is alluvial or less pervious. These are bored hole of 30 cm dia.
up to 10 to 15 m deep, depending on depth of pervious layer. Bore
should be lined with slotted/perforated PVC/MS pipe to prevent
collapse of the vertical sides.
• Percolation Tanks:
Percolation tanks are artificially created surface water bodies,
submerging a land area with adequate permeability to facilitate
sufficient percolation to recharge the groundwater. These can be
built in big campuses where land is available and topography is
suitable. Surface runoff and roof top water can be diverted to this
tank. Water accumulating in the tank percolates in the solid to
augment the groundwater.
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5.Methods of Rainwater Harvesting
Components of the roof top rainwater harvesting
The illustrative design of the basic components of roof top
rainwater harvesting system is given in the typical schematic
diagram.
The system mainly constitutes of following sub components:
• Catchments
• Gutters
• Transportation
• First flush
• Filter
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5.Methods of Rainwater Harvesting
• Catchments
The surface that receives rainfall directly is the catchment of
rainwater harvesting system. It may be terrace, courtyard, or
paved or unpaved open ground. The terrace may be flat
RCC/stone roof or sloping roof. Therefore, the catchment is the
area, which actually contributes rainwater to the harvesting
system.
• Gutters
Channels all around the edge of a sloping roof to collect and
transport rainwater to the storage tank. Gutters can be semi-
circular or rectangular and could be made using material such as
plain galvanised iron sheet, Semi-circular gutters of PVC
material, and Bamboo or betel trunks cut vertically in half.
• Transportation
Rainwater from rooftop should be carried through down take
water pipes or drains to storage/harvesting system. Water
pipes should be UV resistant (ISI HDPE/PVC pipes) of
required capacity. Water from sloping roofs could be caught
through gutters and down take pipe. At terraces, mouth of each
drain should have wire mesh to restrict floating material.
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• First Flush
First flush is a device used to flush off the water received in first
shower. The first shower of rains needs to be flushed-off to avoid
contaminating storable/rechargeable water by the probable
contaminants of the atmosphere and the catchment roof. It will
also help in cleaning of silt and other material deposited on roof
during dry seasons Provisions of first rain separator should be
made at outlet of each drainpipe.
• Filter
There is always some scepticism regarding Roof Top
Rainwater Harvesting since doubts are raised that rainwater
may contaminate groundwater. There is remote possibility of
this fear coming true if proper filter mechanism is not adopted.
This filter is very important in keeping the rainwater in the
storage tank clean. It removes silt, dust, leaves and other
organic matter from entering the storage tank.
Types of filters in practice
Sand Gravel Filter
Charcoal Filter
PVC –Pipe filter
Sponge Filter
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6.Advantages of Rain Water Harvesting
• Provides self-sufficiency to water supply
• Reduces the cost for pumping of ground water
• Reduces soil erosion & flooding in urban areas
• Improves the quality of ground water through dilution when
recharged
• In desert, Rain water harvesting only relief
• Easy to Maintain
• Reducing Water Bills
• Suitable for Irrigation
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7. Disadvantages of Rainwater Harvesting
• Unpredictable rainfall
• Initial high cost
• Regular maintenance
• Certain roof types may seep chemicals or animal droppings
• Storage limits
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8.Conclusion
• Since we cannot produce energy, but we can save it by
preventing wastage
• In the same way we cannot produce water, but save it and
protect our future
• Conservation of water
