Rainwater Harvesting method,Over 70% of our Earth's surface is covered by water More than 97% of Earth’s water is in the oceans, 2% is in ice and glaciers- (Both are unsuitable for human use because of Salinity (Ocean Water) and location (ice caps and glaciers) The total amount of water for which all the people, plants and animals on Earth compete is much less than 1% of the total Rainwater harvesting- Alternative water source- Technology used for collecting and storing rainwater for human use from rooftops, land surfaces Decentralised system – Installed in houses, Institutions, community

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Rainwater harvesting

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Total World Water Supply
Location Water
Volume
(km3)
% of Total
Water
Oceans 1,230,000,000 97.17
Ice caps and glaciers 28,600,000 2.5
Atmosphere 12,700 0.001
Rivers and Streams 1,200 0.0001
Lakes (Fresh water) 123,000 0.009
Groundwater
(Shallow to depth of
0.8 km)
4,000,000 0.31
Department
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 Over 70% of our Earth's surface is covered by water
 More than 97% of Earth’s water is in the oceans, 2% is in ice and
glaciers- (Both are unsuitable for human use because of Salinity
(Ocean Water) and location (ice caps and glaciers)
 The total amount of water for which all the people, plants and animals
on Earth compete is much less than 1% of the total

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Department
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1- Precipitation
2- Infiltration- contributes Ground water sources
3- Transpiration
4- Surface runoff – contributes to surface water sources
5- Evaporation
6 - Condensation
The Water Cycle

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Rainwater harvesting- Alternative water
source
 Technology used for collecting and storing rainwater
for human use from rooftops, land surfaces
 Decentralised system – Installed in houses, Institutions,
community
Department
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and
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Sciences

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Where rainwater harvesting is
particularly attractive ?
– Rural area with no surface water sources
– Supply from surface and groundwater sources cannot
meet the water demand (Urban area)
– Groundwater contaminated with Arsenic
– Household do not have capacity to pay for centralised
water supply system
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Benefit of Rainwater harvesting
Has multiple uses-
– Domestic consumption
– toilet flushing, sprinkling,
– ground water recharge,
– reduces urban storm runoff and associate flooding and
errosion
Low maintenance
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Component of Rainwater harvesting
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Typical Domestic Rainwater Harvesting
System
Source: http://www.eng.warwick.ac.uk/DTU/rainwaterharvesting/index.html
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Ground Catchment System
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Ground
Catchment
System
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Typical Domestic Rainwater Harvesting
System
Source: http://www.eng.warwick.ac.uk/DTU/rainwaterharvesting/index.html
Department
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Conveyance
Gutters and
Downspouts
Gutters are installed to
capture rainwater
running off the eaves of
a building.
Department
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Sciences
Semi-circular gutters of PVC material

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Storage
Storage tank, acts to flatten out any fluctuation
in rainfall and usage allowing water use to be, to
a greater or lesser extent, independent of rainfall.
Types
– Ferrocement tank - cement-rich mortar reinforced with
layers of wire mesh,
– Fiberglass
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Storage Tanks
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PVC
Concrete tanks

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Sizing of storage tank
Demand side approach
A very simple method is to calculate the largest
storage requirement based on the consumption
rates and occupancy of the building.
– Consumption per capita per day, C – 20 litres
– Number of people per household, n – 6
– Longest average dry period – 25 days
Storage requirement = C x n x 25 = 3000
litres
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Quality of rainwater
The quality of rainwater is relatively good but it is
not free from all impurities.
Depends upont type and condition of the
catchments and the storage tank
Dust from the soil, and droppings of birds and
animals could be the source of contamination by
the bacteria.
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Method to enhance quality
The first run off from the
roof should be discarded to
prevent entry of impurities
from the roof.
 In case of difficulties in the
rejection of first flow-
Clean the roof and gutter at
the beginning of the rainy
season
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Method to enhance quality
Cleanliness of roof and storage tank is critical in
maintaining good quality of rainwater.
The storage tank requires cleaning and disinfection
when the tank is empty or at least once in a year.
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Source: http://www.rainharvesting.com.au
Leaf Eater®/Leaf Beater®/Leaf
Catcha®

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Disinfecting Rainwater
Rainwater can be used for drinking, if it is clear, has no
or very little taste or smell and is from well maintained
system
Rainwater may not meet WHO drinking water quality
standards, specifically microbiological quality standards,
hence some disinfection is recommended.
Disinfection can be done by:
– boiling the water in before consumption
– adding chlorine compounds/bleaching powder in
required quantity to the water stored in the tank.
– using slow sand filtration
– solar disinfection (SODIS)
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Rainwater Harvesting from Domed
Stadium in Japan
Source: Zaizen et al. (1999)
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 Rainwater Harvesting and Utilization. An Environmentally Sound
Approach for Sustainable Urban Water Management: An
Introductory Guide for Decision-Makers. IETC-UNEP, Japan.
 Rainwater catchment systems for Household Water Supply
(1991). Environmental Sanitation Reviews No No 32. ENSIC,
Bangkok, Thailand.
 UNEP-IETC (1999) Proceedings of the International Symposium
on Efficient Water Use in Urban Areas - Innovative Ways of
Finding Water for Cities. (8 to 10 June 1999), Kobe, Japan.
 Gould, J. and Nissen-Petersen, E. (1999) Rainwater Catchment
Systems for Domestic Supply. IT Publications, London
 Hasse, R. (1989) Rainwater Reservoirs- Above Ground Structures
for Roof Catchment. GTZ.
 NGO Forum and SDC (2001) Rain Water Harvesting System.
NGO Forum for Drinking Water Supply and Sanitation and SDC,
Bangladesh.
Bibliography
Department
of
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and
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Sciences

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 International Rainwater Catchment Systems Association
http://www.eng.warwick.ac.uk/ircsa/
 American Rainwater Catchment Association
http://www.arcsa-usa.org/
 Centre for Science and Environment (CSE), India
http://www.rainwaterharvesting.org
 Development Technology Unit, School of Engineering,
University of Warwick, UK
http://www.eng.warwick.ac.uk/DTU/rwh/index.html
 Chennai Metrowater, India
http://www.chennaimetrowater.com/rainwaterfaqs.htm
 Rainwater Partnership
http://www.rainwaterpartnership.org/
Web Resources on RWH (1)
Department
of
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and
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 Lanka Rainwater Harvesting Forum
http://www.rainwaterharvesting.com
 International Rainwater Harvesting Alliance
http://www.irha-h2o.org/
 Greater Horn of Africa Rainwater Partnership (GHARP)
http://www.gharainwater.org/
 The Web of Rain
http://www.gdrc.org/uem/water/rainwater/rain-web.html
Web Resources on RWH (2)
Department
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