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1. Environmental Engineering- I
By
Akash Padole
Department of Civil Engineering
Rainwater Harvesting

2. • Need for rainwater harvesting,
• Annual potential,
• Collection of rain water for direct use or ground
water recharge,
• Roof-top rain water harvesting
Contents
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4. What is Rainwater Harvesting?
• Rainwater harvesting is the accumulation and
deposition of rainwater for reuse on-site, rather than
allowing it to run off.
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5. Uses of rain water
• Recharge under ground water
• Gardening
• Livestock
• Domestic and Drinking purpose
• For irrigation purpose
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6. • Recharge under ground water
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7. • Livestock
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8. • Gardening
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9. • Domestic and Drinking purpose
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10. • For irrigation purpose
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11. Need of Rainwater Harvesting
• To overcome the inadequacy of surface water to
meet our demands.
• To enhance availability of ground water at specific
place and time and utilize rain water for sustainable
development.
• To improve ecology of the area by increase in
vegetation cover, etc.
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12. • To increase infiltration of rain water in the subsoil;
this has decreased drastically in urban areas due to
paving of open area.
• To improve ground water quality by dilution.
• To increase agriculture production.
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13. Annual Potential
• The total amount of water that is received in the
form of rainfall over an area is called the rainwater
endowment of that area.
• Out of this, the amount that can be effectively
harvested is called the water harvesting potential.
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14. • Based on various factors, the potential of rainwater
harvesting is calculated by the following formula:
Annual Rainwater harvesting Potential
= Rainfall x Area of catchment x Runoff coefficient
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15. Runoff coefficients for various catchment surfaces
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16. • Broadly there are two ways harvesting rainwater.
i. Surface runoff harvesting
ii. Roof top rainwater harvesting
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17. Surface Runoff Harvesting
• In urban area rainwater flows away
as surface runoff.
• This runoff could be caught and
used for recharging aquifers by
adopting appropriate methods.
• It includes catchment areas from
manmade surfaces, such as roads, or
other urban environments such as
parks, gardens and playing fields.
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19. Roof Top Rainwater Harvesting
• It is a system of catching rainwater where it falls.
• In rooftop harvesting, the roof becomes the
catchments, and the rainwater is collected from the
roof of the house/building.
• This method is less expensive and very effective.
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20. • Components of the Roof Top Rainwater Harvesting
system:
1- Catchment area
2- Transportation
3- First flush
4- Storage system
5- Delivery system
6- Filtration system
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21. 1. Catchment area:
• The surface that receives rainfall directly is the
catchment of rainwater harvesting system.
• It may be terrace, courtyard, or paved or unpaved
open ground.
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22. 2. Transportation:
• Rainwater from rooftop should be carried through
down take water pipes or drains to storage or
harvesting system.
• Water pipes should be UV resistant (ISI HDPE/PVC
pipes) of required capacity
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23. 3. First Flush:
• First flush is 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
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24. 4. Storage system:
• All collected rain water are store in tank or barrels
used.
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25. 5. Delivery system:
• It is a system to delivered of water for uses.
• There are use of pumps to take out water from tank
and deliver for many purpose.
• Water is delivered by pipes.
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26. 6. Filtration system:
• Filters are used for treatment of water to effectively
remove turbidity, colour and microorganisms.
• After first flushing of rainfall, water should pass
through filters.
• There are different types of filters in practice, but
basic function is to purify water
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27. Recharging Ground Water Aquifers
• Commonly used recharging methods are:-
a) Recharging of bore wells
b) Recharging of dug wells.
c) Recharge pits
d) Percolation Tanks
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29. • Recharging of bore wells
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30. • Recharging of dug wells
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31. • Recharge pits
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32. • Percolation Tanks
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33. • In the state of Tamil Nadu,
rainwater harvesting was made
compulsory for every building to
avoid ground water depletion.
• In Rajasthan, rainwater
harvesting has traditionally been
practiced by the people of the
Thar Desert.
• At present, in Pune (in
Maharashtra), rainwater
harvesting is compulsory for any
new society to be registered
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