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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)