new zealand; are rain tanks (rain barrels) part of the answer
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8/3/2019 New Zealand; Are Rain Tanks (Rain Barrels) Part of the Answer
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Jeremy Gabe, Landcare Research
with input from Sam Trowsdale, Eva Vesely, Nalanie Mithraratne, Sumita Ghosh, Robert Vale and Robyn Simcock
Are Rain Tanks Part of the Answer?
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Why do we need to consider rain tanks?
Natural resource constraints
Flood risk management
Degradation of natural urban waters
Economic efficiency
NO CONSTRAIN T FUTU RE SHORTAGES SHORTA GESPubl ic Good Dem and Managem ent Regulat ions
(AT COST) (e.g. METERING) (USE RESTRICTI ONS)
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LIUDD Research Questions on Rain Tanks
How much water can rain tanks supply?
What barriers prevent the use of rainwater inurban areas?
Can rain tanks reduce infrastructure costs?
Do rain tanks reduce impacts on natural urbanecosystems?
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Water Supply How Much?
Typical roofareas (m)
Total water collectionfrom roof (m/ annum)
100 m 112
150 m 168
200 m 224
250 m 280
Using Average Annual Rainfall for Auckland Region: 1244 mm
Sources: Vale and Ghosh (2006); Mithraratne and Vale (2007)
Rainwater Supply Potential
Current consumption = 240 m3/yr
No piping leaks = 211 m 3/yr
Demand Management viatechnical interventions = 180 m 3/yr
Household Consumption Averages(Auckland City)
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Water Supply How Much?Auckland low-rise commercial building: Empirical study (2006)
Source: Trowsdale et. al (2007)
792
726
Potable Water
ToiletFlushing
170390
~356
Loss
1352
2376
CITY SUPPLY
Roof
Raintanks
RAINRAIN
CityStormwater
CitySewerage
668
Glasshouse
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Water Supply - Barriers
Toilet Flushing
Irrigation (e.g. Lawn/Garden)
Laundry/Clothes Washing
Levelofsta
tutory
responsib
ility
High
None
Sources: Vesely et al. (2005); Eason (2007)
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Water Supply Raintank Design
Leaf guards
First Flush Diverters
Regular Maintenance
Filtration/Treatment(for potable supplies)
Graphic: BRANZ
Graphic:MinistryofHealth
Source: Eason (2007)
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Reducing Infrastructure Costs - FinancialDevelopment Scale Empirical Study (Key devices were Rain Tanks)
0
(+0%)
40,000
(+6%)
0
(+0%)
24,000
(+4%)
Difference (LIWS-C)
612,000661,000612,000643,000Low Impact
with water savings (LIWS)
612,000621,000612,000619,000Conventional (C)
10%3.5%10%3.5%Discount Rate
100 years50 years
Life Cycle Costing Conventional vs. LIUDD
Cost Savings New Costs Unquantified Benefits
Reduced downstream SW upgrade Rain tanks (design, procurement, installation) Innovation capacity
Reduced household mains water Future technical flexibilityconsumption
Source: Vesely et al. (2005)
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Reducing Infrastructure Costs - Financial
Concrete rain tank + Mains + DM
Plastic rain tank + Mains + DM
Status Quo(Mains without DM)
Mains + DM (no rain tank)
Plastic rain tank + DM
Concrete rain tank + DM
Source: Mithraratne and Vale (2007)
Household Scale Modelling water supply alternatives
DM = Demand Management technologies
(e.g. Low-flow fixtures)
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Reducing Costs Non-Financial
Source: Mithraratne and Vale (2007)
Household Scale Greenhouse Gas Emissions
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Reducing Costs Non-Financial
Source: Mithraratne and Vale (2007)
Household Scale Energy
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Reducing Impacts on Urban Ecosystems
Source: Trowsdale et. al (2007)
792
726
Potable Water
ToiletFlushing
390170
~356
Loss
1352
2376
CITY SUPPLY
Roof
Raintanks
RAINRAIN
CityStormwater
CitySewerage
668
Glasshouse
Key Mechanism = Capture & Diversion of Stormwater
Actual Performance Potential Performance(All Water Supply met by Rain Tank)
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Reducing Impacts on Urban Ecosystems
Source: Trowsdale et. al (2007)
Key Mechanism = Capture & Diversion of Stormwater
Actual Performance Potential Performance(All Water Supply met by Rain Tank)
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Reducing Impacts on Urban Ecosystems
Source: Trowsdale et. al (2007)
Other Beneficial Uses of Captured Rainwater
Potential Performance(All Water Supply met by Rain Tank)
Groundwater Recharge
Addison Development, Papakura
Urban stream baseflowsupplementation
Self-watering gardens
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Summary
Most NZ urban areas are able to meet theirresidential and commercial building waterconsumption with a rain tank
Water quality improvements can be obtained through
best practice design and maintenance
At the development scale, installation of rain tanks iscurrently cost-neutral, with the potential to deliver
innovation and flexibility for future challenges
At the household scale, water supply from rain tankscosts less than mains delivery, but a hybrid system is
most expensive
The ecological benefit of rain tanks is dependent onthe amount of draw down (consumption)
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