The document discusses rainwater harvesting, emphasizing its importance as a sustainable water resource due to increasing pollution and depletion of traditional water sources. It outlines the methods and components of domestic rainwater harvesting systems, including catchment areas, conveyance, and storage techniques. Additionally, it highlights the advantages and disadvantages of rainwater harvesting, advocating for its adoption in both urban and rural settings.

1. RainWater
Harvesting
By
Deepak Narayan Paithankar
Assistant Professor
Department of Civil Engineering
Sanjivani College of Engineering

2. Key Points of Discussion :
Rainwater harvesting:
Introduction, need, methods and components of domestic rainwater harvesting system. Design of roof top
rainwater harvesting system.

3. INTRODUCTION
The total amount of water on earth remains constant. The rapid growth in
population together with the extension of irrigated agriculture and
industrial development, are putting stress on the natural ecosystems. In
the face of growing problems, society has begun to realize that it can no
longer subscribe to a use and discard philosophy with any natural
resource. One such resource is WATER. To deal with it, a technique called
RAIN WATER HARVESTING was introduced where rain water is used to
meet some of our daily needs.

4. What is Rain Water Harvesting ??
Rainwater harvesting is the accumulating and storing, of rainwater. It has been used to provide
drinking water, water for livestock, water for irrigation or to refill aquifers in a process called ground
water recharge.
Rainwater harvesting is a technology used for collecting and storing rainwater from rooftops, the land
surface or rock catchments using simple techniques such as jars and pots as well as more complex
techniques such as underground checkdams.
It is a method which has been used since ancient times and is increasingly being accepted as a
practical method of providing potable water in development projects throughout the world. It has
wide application also in urban and semi-urban areas where the reliability and quality of piped water is
increasingly being questioned.
Rainwater can be utilized alone or together with other supply sources in residential, commercial and
industrial projects where purewater is desired.

5. Need of Rain Water Harvesting….
Due to pollution of both groundwater and surface waters, and the
overall increased demand for water resources due to population growth,
many communities all over the world are approaching the limits of their
traditional water resources. Therefore they have to turn to alternative or
‘new’ resources like rainwater harvesting (RWH).
Rainwater harvesting has regained importance as a valuable
alternative or supplementary water resource. Utilization of rainwater is
now an option along with more ‘conventional’ water supply technologies,
particularly in rural areas, but increasingly in urban areas as well.

6. Need of Rain Water Harvesting… (Continued…)
 of the total water on earth, only about 2.5%constitutes freshwater. Rest is saline water in
the oceans.
 30.8% of the totalfreshwater on earth is groundwater available upto a depth of 800m
which can be extracted foruse.
Source : https://commons.wikimedia.org/wiki/File:World_water_distribution.png

7. Need of Rain Water Harvesting… (Continued…)
 Surface water is inadequate to meet our demand and we have to depend on ground
water. So to increase the ground water table through artificial recharge and improve
itsquality.
 Over-exploitationof ground water resource has resulted in decline in water
levels in most parts of the country.
 Toincrease soil moisture levels for urbangreenery.
 Toprovide supplemental water for the city'srequirement.
 Tomitigate urban flooding.
 It makes ecological and financial sense not to waste a pure natural resource
available in large quantity on one’s roof.

9. Components of Rain Water Harvesting
Catchment
Delivery
Storage

10. Methods of Rainwater Harvesting

11. Steps of Rainwater Harvesting
1) Catchment:
Any surface or the paved areas can be treated as catchment.
Even the footpaths and roads can act as the catchment, as these
areas too receive the direct rainfall.
Rooftops are the best among them because of the large
coefficient of run off generated from them and there are less
chances of contamination ofwater.

12. 2)Conveyance :
Conveyance system basically includes down pipes which collects the rain water
from catchment to the storage tank. These down pipes are usually built during
the time of construction. They need to be designed appropriately so as to avoid
the loss of water during the conveyance process.
3)Storage :
The storage system is designed according to the amount of water that is to be
stored. The design and site of the storage system should be properly chosen. The
areas which receives the rainfall frequently, there a simple storage system could
be constructed, to meet the daily water requirements. Otherwise the areas which
receive the lesser rainfall, there the storage systems are quite essential. Rain
barrels, underground or open slumps are mostly used to collect rain water. The
storage system should be properly sealed and should not leak. Using chlorine
from time to time keeps the water clean.

13. Methods of Rainwater Harvesting
Storing of rain water on roofs of the houses: Rain water falling on the roofs
of the houses can be stored in nearby wells, tanks and step wells or can be stored
in houses through pipes. The rain water of roofs can also be stored in the water
percolation tanks for recharging groundwater.
Small bonding around the fields: Flow of rain water falling on the fields in
checked by building small bounding around the fields. The water thus stored n the
field percolates underneath and increases soil moisture.
 Step farming: Soil moisture of step fields made along mountain slopes is being
increased by checking rain water of these fields.

14. Check dams on seasonal rivers and drains: Rain water is also stored
behind the check dams constructed over the seasonal rivers and
drains with the help of soil, stones and wood. These dams regulate the
water supply and also help in controlling soil erosion to someextent.
Water percolation tanks: Rain water is stored in tanks constructed in
lands is unsuitable for agriculture. These tanks serve the purpose of
recharging of ground water reserves as water stored onthese.
 Making of drains: Rain water is also being stored in the drains dug
around thefields.

15. Structures generally used in recharging of ground water are:

16. • Pits Recharge: Pits are constructed for rechargingthe shallowaquifers.
• Trenches: These are constructed when thepreamble strata is available at shallowdepths.
• Dug wells: Existing dug wells may be utilized as recharge structure and water should pass through
filter media before putting into dugwell.
• Hand Pumps: The existing hand pumps may be used for recharging the shallow / deep aquifers, if
the availability of water is limited. Water should pass through filter media before diverting it into
handpumps.
• Recharge Shafts: With bore wells for recharging the upper as well as deeper aquifers, lateral
shaftsof 1.5 to 2m wide and 10 to 20m long depending upon availabilityof waterwith one or two
bore wells is constructed. The lateral shafts are back filled with boulders, gravels and coarsesand.
• Spreading Techniques: When permeable strata start from top then this technique is used. Spread
water in streams by making check dams, cement plugs or a percolation pond may beconstructed.

19. Advantages of RWH
• RWH provides a good supplement to other water sources thus relieving pressure on other
water sources.
• It can supply as a buffer and can be used in times of emergency or breakdown of public
• water supply systems.
• Helps reduce the storm drainage load and flooding in the cities.
• It is a flexible technology and can be built to require meets of any range. Also the
construction, operation and maintenance is not very labour intensive in most systems.
• Prevents water wastage by arresting run off as well as prevents soil erosion and mitigates
flood.
• Sustains and safeguards existing water table through recharge.
• Arrests sea-water intrusion and prevents salination of ground water.
• Rainwater harvesting can reduce salt accumulation in the soil which can be harmful to root
growth. When rainwater percolates into the soil, it forces the salts down and away from the
root zone area. This allows for greater root growth and water uptake, which increases the
drought tolerance of plants.
• Rain-water is a clean and pure source of drinking water which requires minimal chemical
treatment as the amount of pollutants are not much.

20. Disadvantages of RWH
• In terms of complex constructions, there is a requirement for high costs, trained
professionals.
• Maintenance costs may add to the monetary burden.
• If not maintained properly then it can cause various problems in terms of algal
or bacterial growth.
• Tanks if not constructed properly might result in leakages and metal tanks may also
lead to problems such as corrosion harming the water quality.
• All these factors might prove harmful and result in various kinds of health issues.
• The system is very much rainfall dependent and hence if there are problems with
the rainfall in the area, it may not be very effective.

21. Probable Questions Likely To Be Asked in Examination….
1. Explain the benefits of rain water harvesting and discuss the different methods of
rain water harvesting.
2. Explain the methods of rain water harvesting.
3. What do you mean by rain water harvesting? Write a necessity of rain water
harvesting system. Draw a sketch of ‘Roof Top Rain Water Harvesting System for a
Bungalow.’

22. References and suggested readings :
• https://theconstructor.org/water-resources/rainwater-
harvesting-components/6739/
• http://www.rainwaterharvesting.org/urban/Components.htm
• https://www.cseindia.org/overview-727

23. Deepak Narayan Paithankar
Assistant Professor
Department of Civil Engineering
Sanjivani College of Engineering
dnpaithankarce@sanjivani.org.in
Blog : http://www.sanjivanisthapatya.blogspot.com
YouTube : Sanjivani Sthapatya