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Rainwater harvesting
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Total World Water SupplyLocation Water
Volume(km3)
% of Total Water
Oceans 1,230,000,000 97.17Ice caps and glaciers 28,600,000 2.5Atmosphere 12,700 0.001Rivers and Streams 1,200 0.0001Lakes (Fresh water) 123,000 0.009
Groundwater(Shallow to depth of 0.8 km)
4,000,000 0.31
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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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1- Precipitation2- Infiltration- contributes Ground water sources 3- Transpiration4- Surface runoff – contributes to surface water sources 5- Evaporation6 - 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
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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
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Conveyance
Gutters and Downspouts
Gutters are installed to capture rainwater running off the eaves of a building.
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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
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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)
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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)
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