Rain Water Harvesting System: An Alternative Water Supply Option for Arsenic Affected Areas of Bangladesh

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Rain Water Harvesting System An Alternative
Water Supply Option for Arsenic Affected Areas of
Bangladesh

• Dr. Md. Mujibur Rahman
• Professor of Civil Engineering, BUET
• Director, ITN-BUET
• 03 January 2006

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Water Cycle
Condensation
Onshore transport 40,000km3
Condensation
Water Vapor
Evaporation and transpiration 71,000 km3
Evaporation 425,000 km3
Precipitation 111,000 km3
Runoff 40,000 km3
Precipitation 385,000 km3
River
Pond
Canal
Lake
Infitration
Ocean
Flow
Groundwater
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Collection Points
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RAINWATER HARVESTING TECHNOLOGY

• Use of RWS dates back to thousands of years,
  e.g., early civilizations of the Middle East and
  Asia, the Mediterranean region and North Africa
• In recent times RWHS is being widely used in many
  parts of the world, particularly in water
  shortage regions of Africa, Australia and Asia
• Examples are Kenya, South Africa, Indonesia,
  Thailand, Central China, South Australia, New
  Zealand, Japan, Germany and in many parts of USA

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Benefits

• Saves Money
• Saves Energy
• Provides control over water source
• Protects from tariff hikes
• Can be kept free from contamination
• Minimizes urban flooding when collected in large
  scale
• Contributes to ecological cause

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• Paradoxically however, we allow rainwater to flow
  over the surface of the earth and cause
  environmental disasters such as
• flooding,
• landslides and
• soil erosion
• while it is possible to harness it for use in
• households,
• agriculture,
• industrial as well as for
• livestock and environmental improvement

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What Constitutes a RWHS

• A catchment surface where the rain water runoff
  is collected
• A delivery system for transport of water from
  catchment to storage reservoir
• A storage reservoir where the rainwater is stored
  for use

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Technical, Socio-economic and Environmental
Feasibility

• Technical Feasibility
• Rainfall and catchment area must be sufficient to
  meet demand
• Design should be appropriate
• Skills should be available locally
• Socio-economic Feasibility
• A real felt need in the community for better
  water
• Designs should be affordable and cost-effective
• The community should be enthusiastic and fully
  involved
• Environmental Sustainability and Health
• Should have positive environmental impact
• Should improve quantity and quality of available
  water
• Should have positive impact on the health of the
  community

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TECHNICAL EVALUATION OF RWHS

• Design of RWHS Components
• Construction methods and materials
• Operation and Maintenance
• Water Quality
• Cost
• Acceptability

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RAINWATER QUANTITY SUPPLY AND DEMAND

• RWHS is feasible when Supply gt Demand
• RWHS may be used as supplementary, partial or
  backup supplies
• Where main or only source, reliability of the
  system becomes critical
• Supply and demand analysis is therefore important
  design consideration
• Rain Water Supply
• Rainfall data for a period of 10 years or more
  mean annual rainfall data may be applied
• When system reliability is critical, minimum
  annual rainfall that will be exceeded 90 of the
  time, should be used

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Monthly average rainfall data of the project area
in Rajshahi(averaged over a period of 30 years)
mm
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TECHNIQUES FOR DETERMINING STORAGE TANK SIZE

• Dry Season Demand versus Supply
• Simplest approach and appropriate where distinct
  dry seasons exist
• Does not take into account variations in
  rainfall ignores rainfall input and catchment
  capacity to fill the tank.
• Graphical Method
• Reasonable estimate of storage requirement
• Mass Curve Analysis
• Involves identification of critical periods in
  data where the difference between cumulative
  runoff volume and cumulative demand are at a
  maximum. This difference represents the maximum
  volume available for future use
• Statistical Method
• Computer Based Methods

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Cumulative monthly roof run-off (m3)Nov-March
Dry period, April-October Wet season
Storage volume required 6.5 m3
6500 litre
Cumulative water demand line
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Different Types of Reservoir
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Important technical questions asked and Responses
from users
Use of stored rainwater? Drinking and cooking
Quantity sufficient? Sufficient for 8 9 months
Water quality satisfactory? Satisfied with water quality no iron / hardness problem etc.
Roof catchment cleaned before rain? Roof cleaned before the rainy season starts
Storage tank disinfected before storage? Storage tank washed with bleaching powder before storage
Health problem from rainwater use? No significant health problem encountered
Operation and maintenance easy? OM easy replacing the filter nets, taps, cleaning tank, roof catchment area.
OM costly? OM inexpensive hardly exceeds Tk. 20/- per annum
Stored water shared with neighbors? Shared with neighbors only during rainy season not during dry period
Water source when tank is empty? Arsenic free tubewells for 3- 4 months
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Construction Costs of Different Types of Storage
Tanks
Type Capacity (Litre) Cost (Taka)
Ferro-Cement Tank/ Jar 500 3200 2,200 5,500
RCC Ring Tank 1000 - 2500 2700 - 4000
Brick Tank 2500 5300
Earthen Motka 1000 500
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WATER QUALITY

• Parameters of significance
• pH
• Turbidity
• TC,
• FC
• Iron
• Zinc
• Calcium
• Magnesium
• Fluoride
• Lead

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pH variation in (typical) tanks made of different
materials
Water Quality Problem pH
April - June 2002
April - June 2003
Oct-Dec 2001
July - Sep 2003
Jan - Mar 2003
Oct-Dec 2000
Jan - Mar 2002
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FC variation with time in (typical) tanks made of
different materials
Oct-Dec 2001
April-June 2002
April-June 2003
July - Sep 2003
Jan - Mar 2003
Oct-Dec 2000
Jan - Mar 2002
FC problems are reduced now a days
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Operation, Maintenance and Monitoring

• User groups of RWHS are well aware about
• Maintenance of the catchment surface, gutter and
  storage tank
• Gutters and tanks are to be cleaned frequently
• First flush for more than 5-10 minutes diverts
  the rainwater and prevents contamination of water
  in the tank
• Regular inspection and repair of systems
• Appropriate tank cover and filter nets on inlet
  and outlet holes protect water quality

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Lessons for Further Improvement of RWHS

• Regular monitoring is to be continued to help
  people for proper operation and maintenance of
  the system.
• Slope of the gutter should be well maintained to
  ensure maximum rainwater run-off to the storage
  tank
• Roof catchment management for better rain water
  quality
• Earthen motka can be promoted as low cost
  alternative for storage tank
• Support for a reliable supply source / option for
  dry months
• Large community storage e.g., at schools may
  serve as a dry months option

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Large catchment for RWHS and community water
supply
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Large roof catchment for community storage
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Some Important Aspects of RWHS in Bangladesh

• Can be a safe water supply option for arsenic
  affected areas
• Arsenic affected people can be benefited from
  drinking rainwater
• Water available near the kitchen for most part of
  the year
• Water collection time saved for more productive
  use
• Water saving attitude developed particularly
  during dry period

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Entrapreneurship Development

• Trained mason in the community
• Business opportunities for the private sector
  making different components
• Business opportunities for the potters making
  clay motka

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Concluding Remarks

• The action research project leads to the
  conclusion that harvesting rain water could be a
  viable option for safe drinking water supply in
  the arsenic affected areas with appropriate
  backup community source for 2 3 dry months of
  the year
• Further efforts are needed, particularly in
  operation and maintenance of RWH units as well as
  capacity building of the local entrepreneurs and
  of the users, for bringing total confidence in
  people that RWHS could be a sustainable safe
  water option

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