Transcript Slide 1

Rainwater Harvesting
For Decision Makers
Environment and Water Resource Department
February 2008
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What Is Rainwater Harvesting?
RWH technology consists of simple systems to collect, convey, and
store rainwater. Rainwater capture is accomplished primarily from
roof-top, surface runoff, and other surfaces.
RWH either captures stored rainwater for direct use (irrigation,
production, washing, drinking water, etc.) or is recharged into the
local ground water and is call artificial recharge.
In many cases, RWH systems are used in conjunction with Aquifer
Storage and Recovery (ASR). ASR is the introduction of RWH
collected rainwater to the groundwater / aquifer through various
structures in excess of what would naturally infiltrate then
recovered for use
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Why Rainwater Harvesting?
Conserve and supplement existing water resources
Available for capture and storage in most global locations
Potentially provide improved quality of water
Supply water at one of the lowest costs possible for a
supplemental supply source.
Capturing and directing storm water (run-off) and
beneficially use it
Commitment as a corporate citizen - showcasing
environmental concerns
Public Mandate (India)
Replenishing local ground water aquifers where lowering
of water tables has occured
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Why Not RWH?
Not applicable in all climate conditions over the world
Performance seriously affected by climate fluctuations that
sometimes are hard to predict
Increasingly sophisticated RWH systems (ASR) necessarily
increases complexities in cost, design, operation,
maintenance, size and regulatory permitting
Collected rainwater can be degraded with the inclusion of storm
water runoff
Collected water quality might be affected by external factors
Collection systems require monitoring and continuous
maintenance and improvement to maintain desired water
quality characteristics for water end-use
Certain areas will have high initial capital cost with low ROI
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Condensation
Let’s take a look at
Precipitation
The Water
Cycle
Evapotranspiration
Evaporation
Infiltration
Surface Runoff
Consumption
Surface Water
Sea water intrusion
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Condensation
Rainfall Definitions
Intensity – Quantity per time of
the rainfall event (mm/hour)
Precipitation
Duration – period of time for the
precipitation event
Consumption
Average Annual and Monthly
Precipitation – Average rainfall
over one year period and
monthly intervals and usually
based on 30 or more years of
data
Surface Water
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Design and Feasibility Criteria
• Collection Area
• Rainfall
• Demand
• Primary Use (Direct Use, Artificial Recharge (AR) or
Aquifer Storage and Recovery (ASR))
• Storage capacity
• Level of Security - risk of the storage tank running dry
Harvesting potential(m3) = Area (m2) X Rainfall (m) X Collection Efficiency
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Collection Area and Characteristics
Measure Area
Runoff Characteristics
– Roof top
– Paved area
– Bare ground
– “Green area”
0.75 – 0.95
0.50 – 0.85
0.10 – 0.20
0.05 – 0.10
Water harvesting potential(m3) = Area (m2) X Rainfall (m) X Collection Efficiency
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Average Annual Precipitation for Mexico
Precipitación Media Anual
DE 0 A 125mm
DE 125 A 400mm
DE 400 A 600mm
DE 600 A 800mm
DE 800 A 1,200mm
DE 1,200 A 1,500mm
DE 1,500 A 2,000mm
DE 2,000 A 2,500mm
DE 2,500 A 4,000mm
MAS DE 4,000mm
Water harvesting potential(m3) = Area (m2) X Rainfall (m) X Collection Efficiency
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Estimate Precipitation Quantity and Timing
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
4.96
2.54
5.08
7.75
5.21
8
6.33
3.12
29.06
36.47
44.27
19.1
(All data in cm)
Monthly average rainfall (cm) on the
island of TCCC
centimeters
50
40
30
Series1
20
10
0
1
2
3
4
5
6
7
8
9 10 11 12
Month
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Feasibility Analysis
Example #1
Roof area = 6000 sq meters
Average Annual Rainfall = 400 mm
Collection Coefficient = 0.90
Potential = 6000 sq meters * 0.4m * 0.90 = 2,160 cu meters/ year
Cost for Water = US $4.00/ cubic meter
Savings = $8,640.00 (does not include maintenance)
Demand = 50,000 cu meter/ month
Supply = 0.4% of demand
Overall Cost to Install = $150,000 (low ROI)
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Feasibility Analysis
Example #2
Roof area = 6000 sq meters
Average Annual Rainfall = 1400 mm
Collection Coefficient = 0.90
Potential = 6000 sq meters * 1.4m * 0.90 = 7,560 cu meters/ year
Cost for Water = US $4.00/ cubic meter
Savings = $30,240.00 (does not include maintenance)
Demand = 50,000 cu meter/ month
Supply= 1.3% of demand
Overall Cost to Install = $150,000 (acceptable ROI?)
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Rain Water as Source Water
Design Considerations
1
2
Typical Diagram Recomendation
3
4
5
6
Raw water
tank or
Aquifer
7
1 Roof
2 Screen
3 Discharge of water
4 Pre-filter
5 Storage tank
6 Flow meter
7 Storm water discharge
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Aquifer Storage and Recovery or
Artificial Aquifer Recharge?
Require complete hydrogeological analysis,
stakeholder engagement and potentially regulatory
approval
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Ground Water Recharge
Under natural conditions it may take days to centuries to recharge ground water
by rain water. As we need to replenish the pumped water, Artificial Recharge of
Ground water is required at some locations.
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Storage
• Storage devices may be either above or below ground
• Different types include
 Storage Tanks
 Water Containers
 Lagoons or Lined Ponds
 Infiltration Ponds
 Size based on rainfall pattern, demand, budget and area
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Percolation Pit
To divert rainwater into an
aquifer,
The percolation pit is covered
with a perforated concrete slab
The pit is filled with gravel/
pebbles followed by river sand
for better percolation.
The top layer of sand must be
cleaned and replaced at least
once in two years to remove
settled silt for improving the
percolation
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Recharge Wells
The runoff water from rooftops or
other catchments can be
channelized into an existing /new
well via sand filter to filter turbidity
and other pollutants
Abandoned wells can also be used
Cost-effective process, which not only
conserves rainwater for immediate
use but also helps to enhance the
local ground water situation
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Quality Issues
Roofs contain: bird droppings, atmospheric dust, industrial and
urban air pollution
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Operational Procedures and Design
Considerations
• Screen to prevent birds, animal and insects;
• Lead based paint must not be used on the roof;
• Tar based roof coatings and materials should not be used
– Phenolics and other organics can leach from materials
• If roofs painted with acrylic paints, new concrete or metal
roofing - first few rainfalls should not be collected to
avoid metals, detergents, and other chemicals
• Clean the gutters and tank every 3 months;
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Operational Procedures and Design Considerations
• Storage tank – dark materials to exclude light and algae
formation
• Corrosion resistant materials
• Tank in protected shaded area – lower temperature
• For multiple storage tanks – design for frequent turnover
• Regional wind direction and industrial activity – Lead,
Mercury, other heavy metals
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Operational Procedures and Design Considerations
• 10 minute purge
• Chlorinate in storage
• Clean tank when not used for long periods
Cl2
Plant
Use
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Initial Water Quality Sampling and Screening
Microbiological testing
• Total coliform
• Fecal coliform
• Heterotrophic bacteria
Inorganic contaminant testing (metals)
Organic chemicals
• Pesticides, Industrial Chemicals, Hydrocarbons
Turbidity
pH
• Acid rain (4.5) is often associated with man-made pollution
• Volcanic activity - sulfur dioxide (SO2)
Frequency – annual or seasonal? Effect on treatment system?
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Final Considerations
Legislation and Regulations in development in most of the
countries in the world
Check on regulatory requirements especially if AR or ASR
Few operational projects all over the Operations System, but
lots of interest showing up –
Use the TCCC Global Rainwater Harvesting Committee for
help and approvals (web site soon?)
Very powerful tool towards sustainability
Safe, once the reccomended practices are fully observed
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Andina Pilot Project
rainfall rates
Rio de Janeiro State
Rainfall rates (12 months) = 1,300 mm
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Andina Pilot Project
Cost-saving analyze
Estimated Calculation model
(estimated for all roof size)
Total volume = rate of rain per year x area (M²)
• 1.3 x 55,700
• 72,410 M³
• 7% total income water
Savings = Total volume (M³) x Cost water (US)
• 72,410 x 3.8
US$ Savings = $275,000/YEAR
Payback less then 1 year
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Andina Project, Brazil
Lateral view
gutters
Rain water pipe
VF-6 Filter
Total investment:
US$ 150,000
October/2006: Under
implementation
Rainwater harvesting
system for 100% of the roof
Discharge the
excess water
Discharge - storm
water system
Pilot Project
Pilot project: 2004/2005
Roof size: 6,000 m2
Collection rainwater from
the gutters
Filtration at filter system
Storage in 5,000-liter tank
Rain water filtered
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Andina Pilot Project
Harvesting system
Cosh VF6 Filter operation:
Rain water distributed across the filter
cascade;
Larger dirt particles are washed across the
cascades;
Pre filtered water flows over a second filter
(mesh size 0.55 mm), low maintenance;
Cleaned water flows to the storage tank;
Dirt goes to the sewer.
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Green Design - Nairobi
SOLAR PANELS
SLOPING GLASS FACADE
WATER TANK
GREEN ROOF
WATER
STORAGE
GREEN ROOF
WATER
STORAGE
POROUS
PARKING WATER
STORAGE
CHILLER UNITS
DEEPLY RECESSED WINDOWS –
FILTERED LIGHT
FACADE –
THERMAL MASS
PASSIVE
COOLING
SYSTEM
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RAIN WATER HARVESTING FOR OFFICES – Developing a GREEN BUILDING
in Nairobi, Kenya
RAIN WATER ACCUMULATION IN LIEU OF STORM WATER ATTENUATION POND
GREEN ROOF
GREEN ROOF
MANICURED
LAWN
GARDEN
Concept & Design Principles
POROUS PARKING
BACKUP MUNICIPAL SUPPLY
OZONATION
FILTRATION
OVERFLOW
GROUND WATER
REPLENISHING
WELLS
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PRINCIPLES OF A GREEN BUILDING - WATER
SYSTEM OF RAIN WATER HARVESTING AND GREY WATER ARE
COMBINED TO ACHIEVE THE FOLLOWING:
• 25% OF POTABLE WATER CONSUMPTION REDUCTION
• 100% OF POTABLE WATER PROVIDED BY RAIN
• 50% REDUCTION OF SEWER QUANTITIES
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Establishing the need in India…
A news article
says that
ground water
levels in New
Delhi are falling
and RWH will
become
mandatory.
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