Rainwater harvesting

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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

• Over 70 of our Earth's surface is covered by
  water
• More than 97 of Earths 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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The Water Cycle
1- Precipitation 2- Infiltration- contributes
Ground water sources 3- Transpiration 4- Surface
runoff contributes to surface water sources 5-
Evaporation 6 - Condensation
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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/rainwater
harvesting/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/rainwater
harvesting/index.html
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Conveyance

• Gutters and Downspouts
• Gutters are installed to capture rainwater
  running off the eaves of a building.

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
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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Leaf Eater/Leaf Beater/Leaf Catcha
Source http//www.rainharvesting.com.au
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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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Bibliography
? 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.
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Web Resources on RWH (1)
? 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.ht
m ? Rainwater Partnership http//www.rainwaterpa
rtnership.org/
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Web Resources on RWH (2)
? Lanka Rainwater Harvesting Forum http//www.ra
inwaterharvesting.com ? International Rainwater
Harvesting Alliance http//www.irha-h2o.org/ ? Gr
eater Horn of Africa Rainwater Partnership
(GHARP) http//www.gharainwater.org/ ? The Web
of Rain http//www.gdrc.org/uem/water/rainwater/r
ain-web.html