Water use and sustainable commercial buildings

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This article presents issues related to water use in sustainable commercial buildings

Summary

For commercial buildings there are four main types of water that need to be considered, these are potable water, greywater, blackwater and stormwater. Potable water is generally defined as 'water which is suitable for human consumption' (Australian Standards, 2003) and is commonly referred to as drinking water. Greywater is the domestic wastewater from bathroom fixtures (such as basins, showers and baths), laundry fixtures (such as clothes washing machines and laundry troughs) and kitchen facilities (such as sinks and dishwashing machines). Depending on the level of wastewater treatment, greywater can be recovered and used for applications such as toilet flushing and irrigation. Blackwater refers to 'waste discharges from the human body' (Australian Standards, 2000), which are collected through fixtures such as toilets, urinals and bidets. It is possible to use this wastewater for non-drinking purposes once treated and disinfected. Stormwater refers to run-off due to rainfall collected from roofs, impervious surfaces and drainage systems (Australian Standards, 2003). Stormwater collected from roofs (also referred to as rainwater) can be used untreated for applications such as wash-down, irrigation and toilet flushing.

The industrial/commercial sector uses around 21% to 30% of the total potable water use in Australian urban centres. Within the sector the largest users of potable water are main retail shops, educational uses, professional offices, and hotels/taverns. Educational facilities are likely to include water use for irrigation of sports ovals and grounds.

Where water is used within a building depends on the building type. For example, the majority of water used in a restaurant is for kitchen applications, whereas for other buildings, such as office buildings, kindergartens and large shopping centres, the majority of water is used in cooling towers. Reducing water consumption in buildings and improving water efficiency is a major aspect of creating sustainable commercial buildings.

The benefits of implementing water efficiency initiatives in buildings may include:

• cost savings in annual water bills, particularly when the price of water is likely to increase, based on the current drought conditions
• adding to the corporate image of a business/organisation
• reduced energy costs and greenhouse emissions
• helping to ensure water is available for future generations.
  
  

Definitions

Types of water

• Potable water
• Greywater
• Blackwater
• Stormwater
• Groundwater
• Embodied water

Potable water

Potable water is generally defined as 'water which is suitable for human consumption' (Australian Standards, 2003) and is commonly referred to as drinking water. Acceptable characteristics of potable water are specifically defined in the Australian Drinking Water Quality Guidelines and in the international World Health Organization (WHO) guidelines for drinking-water quality. Water authorities or retailers usually supply potable water via reticulation systems. When there is discussion on saving water, it usually refers to a reduction in the use of reticulated potable water, also known as 'scheme' water.

'A national guideline for drinking water standards, the Australian Drinking Water Quality Guidelines, was initially published in 1996 and updated in 2004. In Victoria, where potable reticulated water is supplied by a number of local water authorities, requirements for the supply of safe drinking water have been legislated by the state government. In Queensland, potable water is supplied by various municipal councils, and in Western Australia it is provided by a single water authority. Whilst Victoria arguably has the most stringent requirements in relation to the supply of drinking water, there are currently no similar regulations for the supply of water for other end uses. There is currently no national standard for water quality matched to the range of possible end uses.' (DEH, 2006a)

Greywater

Greywater is the domestic wastewater from bathroom fixtures (such as basins, showers and baths), laundry fixtures (such as clothes washing machines and laundry troughs) and kitchen facilities (such as sinks and dishwashing machines). Depending on the level of wastewater treatment, greywater can be recovered and used for applications such as toilet flushing and irrigation. Greywater should not contain human waste or industrial waste. Although untreated wastewater can be used for sub-surface irrigation, it is generally recommended that some level of treatment is provided for most end uses, particularly for commercial and/or public applications. Greywater from kitchens is not usually re-used untreated, as it contains higher levels of fats and oils that require removal with a grease trap, as well as caustic chemicals from dishwasher detergents that may damage soils.

Blackwater

Blackwater refers to 'waste discharges from the human body' (Australian Standards, 2000), which are collected through fixtures such as toilets, urinals and bidets. This wastewater can be used for non-drinking purposes once treated and disinfected. The wastewater can be obtained directly from sewers (sewer mining) and treated on site, or can be obtained from a large treatment plant that collects and treats the wastewater from a sewage system and then pipes it to the re-use location once treated. Re-use of wastewater is heavily dependent on a treated, reliable and safe source, and generally the ideal locations for such re-use projects are close to wastewater treatment plants (City of Greater Geelong, 2006). This recycled water can be used for irrigation and toilet flushing through the provision of a third-pipe network.

Stormwater

Stormwater refers to run-off due to rainfall collected from roofs, impervious surfaces and drainage systems (Australian Standards, 2003). Stormwater collected from roofs (also referred to as rainwater) can be used untreated for applications such as wash-down, irrigation and toilet flushing. Stormwater from surfaces and drainage systems is likely to require treatment due to potential contaminants from the surrounding catchment. Stormwater from surfaces and drainage systems lends itself to treatment using wetlands. Water sensitive urban design (WSUD) refers to treating stormwater run-off from impervious surfaces to improve its quality before re-use or release into the environment.

Groundwater

Groundwater is water that lies beneath the surface of the ground. On a small scale, it can be extracted by drilling a borehole, while on a larger scale it can be extracted by constructing and operating extraction wells. Groundwater can be used for various applications, such as agricultural, municipal and industrial uses (Wikipedia, 2007), depending on its quality.

Groundwater quality varies widely, with the limiting factors for usage being volumes available, recharge rates, flow rates and salt content and contaminants. In many areas, groundwater is highly saline, limiting its beneficial uses (DEH, 2006a).

Embodied water

Embodied water is the amount of water required to manufacture products, including the extraction of raw materials, transporting those materials, and processing them into the final product. Virtually all products we use will have consumed water during their manufacturing process. Determining how much water a particular product has consumed is a complex process that is only now beginning to be understood.

Where is water used?

The amount of water used by the industrial/commercial sector ranges from 21% to 30% of all water used in Australian urban centres (DEH, 2006a). However, this percentage does not separate base building water use and process water use.
There is limited information in Australia about how much water specific public, commercial and industrial buildings use. The figure titled Water consumption in industries shows a breakdown of water consumption across various industry sectors in Sydney — note that this breakdown does not separate base building water use and process water use.

The figure titled Average water demand by sub-sector shows the water consumption of various commercial sub-sectors, as based on a review of data from eight Queensland local government water service providers. It shows that the largest users of water are main retail shops, educational uses, professional offices, and hotels/taverns. Educational facilities are likely to include water use for irrigation of sports ovals and grounds.
There are also large variations in where water is used within a building, depending on the building type. For example, the majority of water used in a restaurant is for kitchen applications, whereas for other buildings, such as office buildings, kindergartens and large shopping centres, the majority of water is used in cooling towers. The table below shows the breakdown of water end use for a number of different commercial/public building types.
Breakdown of water end use for commercial / public building types

Source: Department of Natural Resources, Mines and Water, 2006

The importance of water efficiency

Why is it important?

• Climate change and water security
• Importance for owners
• Importance for developers
• Importance for builders and contractors
• Importance for designers
• Importance for occupiers
• Importance for managers

Climate change and water security

Climate change is an important issue forAustralia's water supplies. Although there is some debate in the media as to the exact severity of climate change, the chemistry and physics behind global warming have been known for over 30 years. What we are now seeing is evidence that climate change is already occurring.

The Water Corporation in Perth has reported a 66% reduction in average inflows into its integrated water supply system over the last ten years (left figure). This is due to a combination of reduced precipitation and increased evaporation as the southern Australian winter rainfall band shifts pole-wards (Flannery, 2005).
Water catchments have a threshold effect where roughly the first 500 mm of rain in a year is lost to evaporation, plant evapotranspiration, and ground infiltration. This means that for years with less than 500 mm of rainfall (such as 2006/07, which was a record-breaking drought over much of southern and eastern Australia), very little rainfall will end up in water supply reservoirs. Climate change is tipping much of Australia past this threshold of exponentially reduced run-off.

The left figure (Moving average rainfall at Melbourne') shows how a long-term decline in rainfall has taken western Melbourne and central Victoria past this 500 mm threshold. Australian cities can generally withstand a drought year because they store about three years worth of water. Australia's reserves of water need to be seven times the size of equivalent European reserves in order to provide the same level of water supply reliability. However, if our reserves of water do not refill or recharge because of climate changes, these large capacities do not help Australian cities to meet water demand. Therefore, to manage the effects of climate change, water efficiency and alternative water supplies are an integral part of the solution.
Under AS/NZS 4360:2004 — risk management, the likelihood and consequences of the water supply impacts of climate change can be classed as extreme. The changes will occur over the same time frame that engineering assets are designed for (i.e. a design life of 80--150 years). Risk management usually aims to reduce catastrophic risk to below one in a million or 0.0001%. Climate change risks over the next 100 years are much higher than this level.
As climate change intensifies, water scarcity is likely to result in further water constraints, and restrictions in southern and eastern Australia will be increased. Water supply constraints and restrictions will also lead to increasing pressure to implement water efficiency and to find alternative water supplies.

Importance for owners

Owners play an important role in implementing water efficiency in buildings, particularly when it comes to base building applications such as cooling towers. Owners can initiate larger projects, such as substituting potable water with alternative water sources, along with technologies that use less water and hence provide a substantial reduction in potable water use in a building.

Importance for developers

The Plumbing Code of Australia stipulates that all renovations and plumbing works in existing and new buildings are subject to water efficiency guidelines. The Code fosters water efficiency by the use of water-efficient fixtures and fittings, but more can be done to ensure appropriate water-saving initiatives are incorporated into works.
The Plumbing Code of Australia sets a threshold for the minimum level of water efficiency a developer must achieve; however, this a generic level across many varying types of developments.

Importance for builders and contractors

During construction of buildings, builders and contractors can implement changes in how they use water. This can include substituting potable water with water of a lower quality for activities such as wetting down roads for dust control. Alternative procedures for the testing of services with water, or the capture and re-use of water used in the testing of services, can also be considered.

Importance for designers

The Plumbing Code of Australia, along with state and territory legislation, sets out the minimum water efficiency measures to be taken when undertaking the design of buildings. BASIX, the NSW sustainability tool, modifies codes to achieve higher levels of water efficiency. When required by building development stakeholders to achieve higher water efficiency targets, designers can use environmental rating systems such as the Green Star and NABERS tools. These tools provide guidance to the designer, and foster innovation to achieve water efficiency goals.

Importance for occupiers

It is important for occupiers to participate in water efficiency initiatives, as there are many initiatives that rely on behavioural change (such as ensuring taps are turned off properly, only turning a dishwasher on when full, and reporting leaks to building maintenance technicians).  Such initiatives can result in significant savings in a building.

Importance for managers

Managers play an important role in leading and/or supporting water-saving initiatives by influencing behavioural change across an organisation, and are also responsible for the implementation and accountability of such initiatives. In addition, managers can set water efficiency targets for a building in regards to fit-outs, upgrades, or when looking for a new premises.

What are the benefits?

• General benefits
• Benefits for owners
• Benefits for developers
• Benefits for builders and contractors
• Benefits for designers
• Benefits for occupiers
• Benefits for managers

General benefits

The benefits of implementing water efficiency initiatives in buildings may include:

• cost savings in annual water bills, particularly when the price of water is likely to increase, based on the current drought conditions
• adding to the corporate image of a business/organisation
• reduced energy costs and greenhouse emissions
• helping to ensure water is available for future generations.

Benefits for owners

Owners of sustainable buildings that include water efficiency measures have an advantage in the marketplace. The Australian Government, along with state and territory governments, is increasingly demanding that owners provide resource-efficient buildings for government operations. Many organisations and tenants are also pushing building owners for resource efficiency upgrades, in recognition of the lower running costs and other benefits that green buildings provide.

Building owners that have driven successful building greening programs gain a corporate reputation boost and the potential to access environmentally screened investment funding.

Water savings can equal cost savings for owners and tenants.

Benefits for developers

Increasingly, businesses and organisations are looking to occupy and/or purchase buildings that are efficient and that incorporate ecologically sustainable design (ESD) principles. ESD principles refer to sustainable design principles that meet the needs of the current generation without impacting on future generations. They include water conservation and efficiency principles. Thus developers and contractors that incorporate water efficiency into a building or development will have a market advantage.

In addition, incorporating such initiatives is likely to be beneficial for the development approval processes required by local authorities and water authorities. Where it can be demonstrated that the development's anticipated water, sewerage, and/or stormwater loads impact less on local authority's infrastructure than a comparable non-ESD development, there exists a potential to negotiate a reduction in contributions to the local authority's head-works charges.

Benefits for builders and contractors

Builders and contractors who manage their water efficiency during construction may gain a competitive lead in the market in projects where building development stakeholders have set specific targets.

Benefits for designers

Current ESD design practices are seeing water-efficient appliances, fixtures and fittings installed in most new buildings, together with rainwater-harvesting systems. Leading practices will see the re-use or harvesting of greywater or, to a lesser extent, blackwater for non-potable uses, especially in apartments and commercial or public buildings.

Designers that position themselves in the market as being capable of delivering triple bottom line sustainable designs, and who provide innovative solutions, will gain advantage over competitors.  Building owners, managers and occupiers in buildings designed using such designers will be able to market the building's ESD credentials in supplying their product or service.

Benefits for occupiers

Working in an environment where water efficiency and sustainability are incorporated into the building can provide a sense of satisfaction and pride to occupiers. Businesses looking for buildings to lease are increasingly requesting buildings that have ESD principles incorporated into them, including water efficiency. Not only does this support a business' sustainability commitment, but also assists in reducing annual water bills.

Benefits for managers

Any improvements in efficiency are beneficial for managers in the long term, particularly as the price of potable water is likely to increase. In addition, newer improved systems can be more reliable. Monitoring of the water supply through building management systems can provide early identification of unaccounted water (leaks). As water awareness becomes more prevalent, occupiers are likely to use appliances more appropriately and to report any leaks/defects as soon as possible to minimise potential water losses.

What are the risks?

There are risks associated with incorporating water efficiency into buildings. Some of these are outlined below.

• Over capitalising: With the current price of water, there are many water efficiency options that, if implemented, have a high payback period or only provide a small return on investment. Undertaking a cost-benefit analysis is beneficial when assessing the feasibility of options; however in such an analysis, consideration should be given to the likely increase in the cost of potable water. The benefits to the corporate image of a business should also be taken into consideration with such options.
• Health risks: Replacing potable water with alternative sources in a public building can pose some health risks. The risk will depend on the source of the water, the treatment process, and the end use. Appropriate approvals and risk management systems will need to be in place for such options.
• Adverse conditions occurring in older buildings: Older buildings are more susceptible to adverse conditions occurring as a result of wastewater flow reduction in sanitary plumbing and drainage systems, and/or changes to the characteristics of the wastewater. These conditions in the pipe work may compromise the health of the building's occupants.  Consideration needs to be given to the possible effects that these changes may have on the safe operation of the sanitary systems.
• Unproven new technology: New technologies to improve water efficiency in buildings are continually emerging, such as different types of greywater systems and waterless urinals. Implementation of new technologies may prove unsuccessful and thus assurances/warranties will need to be obtained from the suppliers.
• Market and social acceptance: There are alternative technologies that may provide great results in water efficiency, but which may not be widely accepted.  An example is the composting toilet that has been used for many years in places such as caravan parks. Although the technology has improved by reducing odours and improving aesthetics, composting toilets are still not widely used or accepted in public buildings. Such options, if considered appropriate, will need to be implemented alongside an educational and marketing campaign.
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Sources of major impact on water use in buildings

Cooling towers

Cooling towers are a component of some buildings' cooling systems. Where installed, cooling towers can account for up to 30% of the total water used in an average building; a statistic that is even higher in summer (DEH, 2006a). In shopping centres, this figure can be as high as 60% (DNRMW, 2006). 'Water is used in cooling towers by evaporation (which provides cooling), bleed (to prevent build-up of dissolved and suspended solids), drift (water droplets entrained in exhaust air), splashes, overflow, and leaks' (DEH, 2006a). Current benchmarking practice for water use in a cooling tower system is 0.8 kilolitres (kL) per square metre, per annum (Sydney Water, 2006). Cooling tower systems are very dynamic, and treatment of the water is required to control microbial growth, scaling, corrosion and fouling.
Optimum water efficiency in cooling towers depends on the quality of the incoming water. When choosing a water treatment service provider to determine your water treatment program, you should request that water conservation is included as a key performance indicator. AIRAH (Australian Institute of Refrigeration, Air-Conditioning and Heating) holds a register of accredited water treatment companies — see http://www.airah.org.au/spe_wat_man.asp for more information.

Sanitary fixtures

Sanitary fixtures in public, commercial or industrial buildings include toilets, urinals, basin taps, and showerheads. In Sydney, approximately 37% of total commercial building water use is used for domestic/bathroom applications in commercial or public office buildings (DEH, 2006a). This can be much higher, depending on the building type.  While part of this will be for water used in kitchens, the majority is likely to be for sanitary fixtures.

Leakage

'Leakage can be a significant cause of water loss in building plumbing systems — undetected below ground, as well as through dripping taps and toilet cisterns. Rates of water loss vary significantly depending on the type and severity of the leak. As a general guide, dripping (not running) taps can lose between 3--27 L/day, while leakage from toilet cisterns can range from 10 L/day for barely visible leaks to 260 L/day or more for leaks large enough to be visible and/or have an audible refilling hiss. System leaks which are not easily detectable by occupants can be significant.' (DEH, 2006a)
Water audits undertaken by Sydney Water of commercial buildings showed that leaks can account for up to 26% of the building's total water use (DEH, 2006a).

Gardens

Outdoor water use in a typical residential home could be anywhere between 25% to 50% of the building's total water use (DEH, 2006a). A non-residential building's garden water use is likely to vary greatly, depending on the area of irrigated gardens. For example, a hotel resort or public building with large irrigated lawns is likely to have a higher garden water requirement than a city office block. There is little information on the amount of water used on gardens in a commercial building, although a study undertaken by Sydney Water indicates that garden water use is as low as 1% of the total building water use for a typical commercial building (DEH, 2006b), and is about 3% to 4% for a typical hotel in Sydney (Sydney Water, 2001).

Sprinkler testing

The testing of fire sprinkler systems is an important and necessary part of a building's maintenance program. However, sprinkler testing can use large quantities of water that are generally taken from the portable water supply. Research done for the CH2 Building in Melbourne (an average ten-storey building) showed that sprinkler water testing used about ten KL of water per week (RMITUniversity, 2006). This water can be captured for re-use and preferably used for potable purposes.

Policies, regulations and standards

Water regulation inAustralia is diverse, as water is primarily a state government responsibility.  Each state has varying systems for the delivery of reticulated water and varying requirements for water efficiency. There is however a range of national standards and initiatives that influence how water is supplied in Australia. These include the Australian Standards and the National Water Initiative, as detailed below.

Drivers for water policy and standards development on a national scale include:

• the ongoing implications of the current drought and future implications of climate change
• the continuing national imperative to increase the productivity and efficiency of Australia's water use
• the need to service rural and urban communities
• the need to ensure the health of river and groundwater systems, including by establishing clear pathways to return all systems to environmentally sustainable levels of extraction (Commonwealth of Australia, 2005).
  

Water regulations

• What current water regulations exist?
• What is driving water regulation development?
• Future regulation impacts on developments

What current water regulations exist?

Water Efficiency Labelling (WELS)
WELS provides mandatory water-efficient labelling for appliances, including showerheads, washing machines, flow controllers, dishwashers, toilets, taps and urinals (DEH, 2006c). WELS-labelled products are given a water efficiency star rating from one to six.

WELS is enforced through the Australian Government's Water Efficiency Labelling and Standards Act 2005 (the WELS Act) and the AS/NZS 6400:2005 — water-efficient products, rating and labelling.

For more information about water ratings, see http://www.waterrating.gov.au

Building Code of Australia (BCA)
The Building Code of Australia (BCA) contains the technical provisions for the design and construction of buildings in Australia. It is maintained through the Australian Building Codes Board (ABCB). The Building Code generally applies to the building's fabric and construction, while also setting some energy efficiency benchmarks. It does not set benchmarks for water consumption.

Victorian building legislation enforces water efficiency through the five-star legislation. It specifies that a new residential building must have at least a solar hot water service, a rainwater tank, or a greywater system. It also specifies that water-efficient showerheads and taps must be used.

Queensland's Development Code sets water-saving targets for all new domestic buildings to assist in the reduction of potable water demand.

Plumbing Code of Australia
The Plumbing Code of Australia was developed by the National Plumbing Regulators Forum (NPRF) on behalf of Australian state and territory governments. It applies whenever a plumber works on a building, so it is applicable to bathroom and kitchen renovations and refits. The Plumbing Code is designed to fit with both the BCA and Australian standards. One of its objectives is to foster energy and water conservation. For example, under the Plumbing Code, only dual-flush cisterns can now be installed in Australia. These dual-flush toilet provisions were introduced gradually over 12 years, resulting in a 70% reduction in water used for flushing where 6/3 litre flush toilets are installed. The Plumbing Code, like the Building Code, is given legal effect through state legislation.

What is driving water regulation development?

'The regulatory context of water in Australia is currently in a state of rapid change and evolution. Climate change, droughts, growing populations and environmental constraints have put pressure on water regulators to reassign and rethink how water is managed. However, much of this rework of the Australian regulatory context is currently in progress.' (Sustainability Victoria, 2007)

Future regulation impacts on developments

Future changes to regulations, such as changes to requirements for new buildings or renovated buildings, could impact on developments in the following ways:

• Engineers, builders, plumbers and other related technicians will require more training, support, and guidelines.
• Regulations will increasingly drive the water efficiency market, and hence the costs to implement water efficiency initiatives are likely to decrease over time.
  

Water policies

• What current water policies exist?
• Future policy impacts on developments

What current water policies exist?

The National Water Commission
The National Water Commission is responsible for helping to drive national water reform and advising the Prime Minister and state and territory governments on water issues. The Commission is also responsible for managing the implementation of the National Water Initiative (NWI) — the blueprint for national water reform — and for implementing two programs of the Australian Government Water Fund — the Water Smart Australia program and the Raising National Water Standards program (Sustainability Victoria, 2007).

For more information about these programs, see http://www.nwc.gov.au.

Water recycling policies and guidelines
National guidelines for water recycling have been developed under the auspices of the National Water Quality Management Strategy (NWQMS) to provide guidance on best practices for water recycling. These guidelines provide a generic risk-assessment and management framework that is applicable to all types of water recycling. They also provide specific guidelines for the uses of recycled water. Phase one of the guidelines has been completed, and focuses on:

• large-scale treated sewage (blackwater) and greywater to be used for:
  • residential garden watering, car washing, toilet flushing and clothes washing
  • irrigation for urban recreational and open space, agriculture and horticulture
  • fire protection and fire fighting systems
  • industrial uses, including cooling water
• greywater treated on site for use for residential garden watering, car washing, toilet flushing and clothes washing (DEH, 2006a).

Phase two of the guidelines is currently under development, and will focus on stormwater re-use, managed aquifer recharge, and recycled water for drinking.
Each state or water authority has, or is developing, its own set of guidelines and policies, as listed below.

• Western Australia: Code of Practice for the Re-use of Greywater in Western Australia (2005)
• New South Wales: Greywater re-use in sewered single domestic premises (NSW Health, 2000)
• Victoria: Re-use options for household wastewater, EPA Victoria publication 812.1 (2006)
• Queensland: Queensland Plumbing and Wastewater Code (2006) and Queensland water recycling guidelines (2005)
• South Australia: Draft guidelines for on-site domestic greywater systems  (Department of Health, October 2006)
• ACT: Greywater use - guidelines for residential properties in Canberra (2004)
• Northern Territory: Greywater re-use in single domestic premises — information bulletin (Department of Health And Community Services).

Future policy impacts on developments

Future changes to policies could impact on developments in the following ways:

• High water-using businesses could be required to have water management plans in place. This is likely to require more investment in water efficiency implementation.
• An increase in water pricing will impact on developments that do not undertake water efficiency initiatives, but will benefit those that do.
• Policies that relate to alternative water sources will provide direction for substituting potable water in developments.
• Policies that relate to funding opportunities, incentives or rebates will be beneficial to developments implementing water efficiency initiatives.

State and local government urban water initiatives
Low rainfall and an increasing awareness about potential water scarcity have generated a range of water conservation initiatives by state and local governments and water authorities (see table titled 'Water conservation initiatives implemented by state and territory governments' below).

Currently, most of these regulations and initiatives relate to residential dwellings; however, it is likely that future regulations and initiatives will apply to public, commercial and industrial buildings.

Water conservation initiatives implemented by state and territory governments

'Within states and territories, there is a diverse set of regulatory regimes and voluntary programs that have been implemented. Some examples of these measures are detailed below. Note that the success of the use of mandatory water restrictions is being analysed by the National Water Commission and is not addressed here.

National

• The introduction of a mandatory National Water Efficiency Labelling Scheme and water efficiency requirements for toilets (from 1st July 2006)
• All new building developments must include water pressure limiting devices or other means to restrict water pressure to below 500 kPa, (now enforced via AS/NZS 3500.1)
• The introduction of NABERS (National Australian Built Environment Rating System), a performance-based rating system for existing buildings.

New South Wales

• The introduction of BASIX, a performance measurement tool for residential dwellings requiring that potable water consumption for all new dwellings be reduced by up to 40 per cent (the actual amount depends on the climate at the dwelling's location)
• The anticipated introduction of Retrofix requiring that from July 2007, all homes sold that are not water efficient are retrofitted with AAA rated water efficient fittings and fixtures.

Victoria

• Permanent water saving rules for Melbourne that include bans on fountains that do not re-circulate water, and restrictions on times that watering systems can operate
• Water efficient plumbing fixtures are to be installed in new buildings or when fixtures are replaced in existing buildings
• New homes must be fitted with a solar powered hot water system, rainwater tank with a minimum capacity of 2000 L, or a connection to a recycled water supply for toilet flushing and garden watering.

Queensland

• All new residential dwellings and major renovations must include a 6/3 dual flush toilet and 3 A rated shower roses * Mandatory water saving targets with the use of rainwater tanks, communal rainwater tanks, dual reticulation and stormwater re-use
• Local government has the power (under the planning scheme) to determine whether rainwater tanks are required on all new homes. For example, the Gold Coast Council has made this requirement mandatory
• Amendment of the Plumbing and Drainage Act 2002 to allow householders in single dwellings (in sewered areas), with local government approval, to use greywater from the bathroom and laundry for garden watering by subsurface irrigation. However, greywater can not be stored on site untreated
• Water management plans for cooling towers are now required.

South Australia

• Most new homes will require rainwater tanks plumbed to the house to meet non-potable water needs
• Dual flush toilets are required for new homes and replacement toilets.

Western Australia

• Household grey water re-use is permitted through bucketing or an approved re-use system.' (DEH, 2006a)

Water pricing
'Water has traditionally been delivered to buildings at a low cost, which does not factor in environmental, social, and resource constraints. Future pricing reforms could reward water conservation. Pricing mechanisms have been introduced in Victoria for residential customers. The introduction of step tariffs to reward water conservation is intended to drive consumers to better practices (WaterSmart, 2006). The price for each step tariff for residential customers varies slightly for each water utility but is currently:

• Step 1 (0--440 litres per day): $0.78 per kilolitre
• Step 2 (441--880 litres per day): $0.92 per kilolitre
• Step 3 (881+ litres per day): $1.36 per kilolitre.

The issues around water pricing are being examined by the National Water Commission and a review of water pricing in Victoria is currently underway for non-residential customers.' (DEH, 2006a)

Water standards

• Australian standards
• Standards for recycled water

Australian standards

The Australian standards for plumbing and water products are outlined in Section G of the Plumbing Code of Australia. These provisions apply to new installations, as well as to alterations, additions and repairs to existing installations. The Plumbing Code of Australia references AS/NZS 3500.1. AS/NZS 3500.1 was amended in November 2005 to be consistent with the WELS scheme. Water efficiency is enforced in different ways in AS/NZS3500. For example, AS/NZS 3500.1 now specifies that the maximum flow rate from a shower, basin, and kitchen sink or laundry trough outlet shall not exceed 9 L/min.
The AS/NZS 3500 suite of standards include the following codes:

• AS/NZS 3500.1:2003: This specifies the requirements for the design, installation and commissioning of cold water services from a point of connection to the points of discharge, and non-drinking water from a point of connection to the points of discharge.
• AS/NZS 3500.2:2003: This specifies the requirements for the design and installation of sanitary plumbing and drainage from the fixtures to a sewer, common effluent system or an on-site wastewater management system, as appropriate.
• AS/NZS 3500.3:2003: This covers materials, design, installation and testing of roof drainage systems, surface drainage systems and subsoil drainage systems to a point of connection.
• AS/NZS 3500.4:2003: This sets out the requirements for the installation of heated water services using drinking water. It includes aspects of the installation from, and including, the valve(s) on the cold water inlet to any cold water storage tank or water heater and the downstream fixtures and fittings.
• AS/NZS 3500.5:2000: This sets out the requirements for the installation of hot and cold water supply, sanitary plumbing and drainage, and stormwater drainage, for domestic plumbing work.

There are various other Australian standards that relate to water efficiency or alternative water supplies, such as the WELS standard AS/NZS 6400:2005 outlined in the Appliance efficiency section of this article.
More information about water standards can be found at:

• Standards Australia: http://www.standards.org.au
• SAI Global:http://www.saiglobal.com

Standards for recycled water

The on-site domestic wastewater systems covered by AS/NZS 1547:2000 include both primary and secondary wastewater treatment units and associated land application systems. The standard does not cover the direct application of greywater onto land, nor does it provide details of greywater diversion systems. It does however give specific details for wastewater treatment systems for domestic waste, blackwater and greywater, and specific details for land application and absorption systems, including conventional trenches and beds, evapotranspiration systems, mounds and irrigation areas. These are currently regarded as the most commonly used systems and are used as examples throughout the standard.

Most states and territories have specific guidelines for the recycling of wastewater — refer to the Greywater recycling and Blackwater recycling sections of this article for further information.

Measures and assessment

National water intensity benchmarks

National water intensity benchmarks have been developed for office buildings and public buildings. These benchmarks, referred to as NABERS benchmarks, identify what are average, better and best practice water intensities for these building types (See table below). Water intensity refers to the water consumed per square metre of space. Similar work has been conducted in public buildings in the United Kingdom as part of the Water Mark program. The benchmarks provide guidance to building owners, managers and tenants on how their buildings measure up against similar sites nationwide.

Information on benchmarks for other public or commercial buildings is limited, although a small study undertaken by the Department of Environment and Heritage for public buildings showed similar results to the benchmarks for office buildings (DEH, 2006b). Furthermore, 'new benchmarks are being developed for hospital water use, and benchmarking is planned for water use in schools' (Australian Government, 2007).

City West Water, South East Water and Yarra Valley Water have developed benchmarks for various commercial sectors. This information can be accessed from http://www.citywestwater.com.au/business/docs/Benchmarking_Fact_sheets_-_ALL_Feb07.pdf

HVAC efficiency

There are currently no water efficiency standards for measuring and assessing heating, ventilation and air-conditioning (HVAC) systems.

AIRAH is currently developing a nationally recognised training course in the water-efficient operation of cooling tower systems for facility mangers, water treatment personnel and service personnel, and this due for completion by the end of 2007. Also, AIRAH is working with stakeholders to address the issue of water efficiency standards in cooling tower systems.

Appliance efficiency

The water efficiency rating of new appliances is now provided as part of the mandatory WELS scheme. Appliances included in this scheme are:

• clothes washing machines
• dishwashers
• flow controllers
• water closet fixtures
• showers
• tap equipment intended for use over a kitchen sink, bathroom basin, laundry tub or ablution trough
• urinal equipment.

'WELS products are tested at 150, 250 and 350 kPa. Where a building has a water pressure of less than 150 kPa, then a lesser WELS rating fitting may be required to ensure that amenity is maintained.' (DEH, 2006a)

WELS ratings for various appliances are provided in the following tables.

AS/NZS 6400 (WELS) rating specifications – toilet suites

Rating unit	1 star	2 stars	3 stars	4 stars	5 stars	6 stars
L/flush (average flush volume)	>4.5 but not >5.5	>4 but not >4.5	>3.5 but not >4	>3 but not >3.5	>2.5 but not >3	Not >2.5

Showerhead ratings and corresponding flow rates

Rating unit	0 stars (Warning)	1 star	2 stars	3 stars	4 stars1	5 stars1	6 stars2
L/minute	>16	>12 but not >16	>9 but not >12	>7.5 but not >9	>6 but not >7.5	>4.5 but not >6	>4.5 but not >6

1. If the shower complies with all the requirements of AS/NZS 3662 (including the comfort test), and compliance with force of spray requirements.
2. If the shower complies with all the requirements of AS/NZS 3662 (including the comfort test), and compliance with force of spray requirements and having bonus water saving features (e.g. a sensor with auto shut-off).

AS/NZS 6400:2005 – tap flow regulators

Rating unit	0 stars (Warning)	1 star	2 stars	3 stars	4 stars	5 stars	6 stars
L/minute	>16	>12 but not >16	>9 but not >12	>7.5 but not >9	>6 but not >7.5	>4.5 but not >6	not >4.5

Note: Flow rates specified in this table may, in some cases, be lower than requirements for water flow rates at outlets as specified in AS/NZS 3500.1 for the flow rates to taps and cisterns. The flow rates specified in AS/NZS 3500.1 are for the sizing of water pipes for water installations to ensure adequate supply to an outlet, whereas the flow rates in this table are the desirable levels of efficiency for use of the various outlets.

AS/NZS 6400 rating specifications – clothes washers

Rating unit	0 stars (Warning)	1 star	2 stars	3 stars	4 stars	5 stars	6 stars
L/kg of dry load	>30	>21 but not >30	>14.7 but not >21	>10.3 but not >14.7	>7.2 but not >10.3	>5 but not >7.2	not >5

AS/NZS 6400:2005 rating specifications – dishwashers

Place settings	1 star	2 stars	3 stars	4 stars	5 stars	6 stars
Baseline	2.5	2.06	1.7	1.4	1.16	0.96
1	4.1	3.38	2.79	2.3	1.9	1.57
2	5.7	4.7	3.88	3.2	2.64	2.18
3	7.3	6.02	4.97	4.1	3.38	2.79
4	8.9	7.34	6.06	5	4.12	3.4
5	10.5	8.66	7.15	5.9	4.86	4.01
6	12.10	9.98	8.24	6.79	5.61	4.62
7	13.7	11.3	9.32	7.69	6.35	5.24
8	15.3	12.62	10.41	8.59	7.09	5.85
9	16.9	13.94	11.5	9.49	7.83	6.46
10	18.5	15.26	12.59	10.39	8.57	7.07
11	20.1	16.58	13.68	11.29	9.31	7.68
12	21.7	17.9	14.77	12.18	10.05	8.29
13	23.3	19.22	15.86	13.08	10.79	8.9
14	24.9	20.56	16.95	13.98	11.53	9.52
15	26.5	21.86	18.04	14.88	12.28	10.13
16	28.10	23.18	19.13	15.78	13.02	10.74

Note: If a dishwasher achieves less than 1 on the star rating index, the rating of the dishwasher is zero stars.

The Smart Approved Watermark is for outdoor applications and includes products under the following categories:

• Auto
• Cleaning
• Gardening
• Greywater systems
• Household plumbing
• Pools and spas
• Rainwater harvesting
• Watering
• Other (education and synthetic grass)

These products are assessed and approved by an independent panel. Unlike the WELS scheme, they are not given a rating.

Opportunities for improving performance

HVAC opportunities

• Evaporative cooling
• Air-cooled refrigerative systems
• Cooling towers (water-cooled air-conditioning systems)
• Designing/modelling of HVAC
• How to improve existing HVAC systems

Evaporative cooling

Evaporative coolers cool air through moisture evaporation. Systems range from small portable units that must be manually filled with water, up to very large ducted systems, which are the most common in businesses (Synergy, 2006).

Evaporative coolers are more energy-efficient than refrigerative coolers, provide an inflow of fresh air, and are suitable in buildings with poor air sealing or where doors must be left open, as is often the case in retail businesses (Synergy, 2006). The downside to evaporative cooling systems is that they are more suited to dry, hot climates and less suited to humid climates. They can also use a significant amount of water: 'evaporative air-conditioners consume water in two ways; the evaporation of water from the pads which cools the air, and the dumping/bleeding-off of water to reduce the mineral concentration in the sump' (GHD, 2003).

Air-cooled refrigerative systems

Air-cooled refrigerative air-conditioning systems do not use any water; however, they are relatively energy intensive. Once a certain capacity of system is reached, it is less cost-effective to use air-cooled systems in a commercial building, and other types of system configurations need to be considered (Archibald, J. and Gavelis, M., 2002).

As well as providing air-conditioning, most reverse-cycle systems are extremely efficient sources of heating. Also, as a result of the air-conditioning process, condensate is produced, which is a potential alternative water supply. Another consideration is the embodied water of power generation. Coal power stations may use as much as two to five litres of water per kilowatt hour of power produced, representing a large proportion of the water used by air-conditioning over its life cycle.

Cooling towers (water-cooled air-conditioning systems)

'Water is used in commercial building air-conditioning systems as a means of transferring heat, and is lost from cooling towers through evaporation, bleed, drift, splash and overflow.' (DEH, 2006a)

Alternative heat-rejection systems include:

• air-cooled chillers (although these take up more floor space than water-cooled chillers)
• liquid coolers (dry and evaporative)
• variable volume refrigerant systems
• refrigerant air-conditioners
• adsorption chillers, powered by natural gas
• ice storage and chilled water storage systems
• ground source geothermal systems, where cooling water is passed through long loops buried underground
• water source geothermal systems, which directly or indirectly use underground storage aquifers
• sea or lake water cooling (e.g. Sydney Opera House uses sea water for cooling (Sydney Water, 2006))
• hybrid systems
• night sky cooling (Esmore, 2005).
  Left figure: Air-cooled chiller (Source: Sydney Water)
  Right figure: Schematic of ground source geothermal system (Source: Sydney Water, 2006)
  

  

  
  

  
  Alternative heat-rejection systems have the potential to reduce evaporative cooling water usage by up to 100% (DEH, 2006a). However, depending on the type of generation plant supplying power, increases in electricity may result in higher water consumption at the power plant.

Designing/modelling of HVAC

The following building design options will result in less cooling being required, and therefore less water being used in cooling towers or evaporative air-conditioners:

• Reduce the heat load - this can be achieved through following the well-accepted principles of solar passive design, careful selection of materials, and management of the indoor environment, including occupancy levels and energy-efficient equipment.
• When outside air conditions are favourable, use an outside air economy cycle instead of relying solely on the air-conditioning plant.
• When outside air conditions are favourable, use a hybrid-type air-conditioning system involving a natural ventilation system through openable windows.
• Design the building layout to use passive or convection cooling ventilation (DEH, 2006a).
  Parliament House, Canberra
  Parliament House in Canberra has installed a heat exchanger to capture waste heat from a large data centre and use it to heat swimming pool water, reducing energy consumption, saving money and also saving water through a reduced cooling tower load and water use.

  Source: DEH, 2006

  
  

How to improve existing HVAC systems

Evaporative coolers
There is little opportunity for reducing water consumption through evaporation of water to cool the air without loss of function and efficiency. A Queensland study (GHD, 2003) estimates the water used in dumping and bleeding off to range from 8 to 27 kL per household per annum, depending on the location. Opportunities to reduce this water loss are mainly through alternative operation methods, such as:

• replacing evaporative cooling systems with refrigerative systems. However, refrigerative systems are much more energy-intensive
• not bleeding off any water from the evaporative air-conditioner (this is common in MountIsa). However, this option requires more frequent servicing and cleaning
• treating the water being supplied to the evaporative air-conditioner to reduce scaling. This option involves an additional cost and regular servicing, but involves easier cleaning and the pads last longer
• treating and recycling cooling water. Water may be suitable for a lower grade use, such as toilet flushing
• switching to automatic sump dump systems, where water is automatically dumped when salt content becomes excessive. This option uses much less water than bleed-off systems
• reducing the cooling load on the plant by upgrading the building fabric (e.g. by shading or tinting northern and western windows)
• reducing the size of the sump so that a smaller amount of water is dumped each time
• exploring the viability and water use of two-stage coolers, which use an air-to-water heat exchanger to reduce the incoming air temperature without raising humidity before passing the air through a direct evaporation stage to further cool the air (DEH, 2006a).

When deciding on the above, consideration needs to be given to the advantages and disadvantages of each item.

Cooling towers
The table below lists some ways to reduce water usage in cooling towers.

Water savings target	Water savings option
Reduce uncontrolled water losses	Regular checks and services using an accredited water treatment company Install drift eliminators Install anti-splash louvres or splash mats
Reduce controlled water losses	Automatic bleeds to occur when the conductivity is too high (specialist advice from an accredited water treatment company required) Increase the cycle of concentration (ratio of concentration of dissolved solids in condenser water to that of the make-up water)
Other	Use of bypass valves to enable condenser water from chiller to by-pass the cooling tower and return directly to the chiller, thus reducing losses Capture bleed-off in a backwash holding tank and use to backwash side stream filters — monitor use by sub-metering and regular maintenance Reduce the cooling load on the plant by upgrading the building fabric (e.g. shading or tinting northern and western windows) Introduce occupant/behavioural measures to reduce cooling plant demand, such as increasing the temperature set-point from 22 to 26 degrees during summer.

Source: Sydney Water, 2006

A recent development in cooling system technology is the use of in-ground heat source pump (IGHSP) cooling systems: 'the IGHSP cooling system utilises the earth below the ground surface as the heat source and sink. As a result, the water consumption is significantly reduced without the usual decrease in energy efficiency that can result from air-cooling systems. Although the initial cost of installing the system is higher than the water-based cooling system, the operating cost in relation to water and energy use, is significantly lower' (Rafferty, 1997). The hydro-geological features of the site are important in determining the feasibility of the system (Chanan et al., 2003).

Appliance and fixtures opportunities

• Selecting the right appliances
• Toilets
• Urinals
• Taps

Selecting the right appliances

Mandatory labelling currently applies to indoor water-using appliances and fixtures through the WELS scheme. Voluntary labelling is available for outdoor water-using equipment through the Smart Approved WaterMark scheme.

Water Efficiency Labelling (WELS)
WELS provides mandatory water-efficient labelling for appliances, including showerheads, washing machines, flow controllers, dishwashers, toilets, taps and urinals (DEH, 2006c).

WELS-labelled products are given a water efficiency star rating from one to six. WELS is enforced through the Australian Government's Water Efficiency Labelling and Standards Act 2005 (the WELS Act) and AS/NZS 6400:2005 — water-efficient products, rating and labelling. 

Smart Approved WaterMark
Voluntary labelling for outdoor water-using products is undertaken through the WSAA-initiated Smart Approved WaterMark scheme, which is managed by the Australian Water Association, the Irrigation Association of Australia and the Nursery and Garden Industry Association of Australia, with funding from the Australian Government's Smart Water program (DEH, 2006a).

Toilets

Dual-flush toilets
A significant way to save water in buildings is to replace existing single-flush toilets with dual-flush toilets: 'an old-style single-flush toilet could use up to 13 litres of water per flush. Current standard dual-flush toilets use only three litres on a half-flush' (DEH, 2006c). Dual-flush toilets have become standard or mandatory for new buildings in all places around Australia. The most common dual-flush toilet is the 6 litre full flush/3 litre half flush, although a 4.5/3 L dual-flush toilet is now available.

All new buildings should be designed with dual-flush toilets as a minimum. Retrofitting of existing buildings will require advice from a plumber to ensure the correct pressure and plumbing, particularly in a multi-storey building.

Waterless toilets

Although not very common for commercial buildings, urine-separating toilets separate the waste at the source, and as in composting toilets, they reduce the nutrient load on the wastewater treatment system, since approximately 90% of the nutrients in human waste are in the urine (White, 2001). These toilets are a fairly new concept in Australia, but are quite common in Scandinavia, and have water-efficiency benefits as well as nutrient reduction. Composting toilets are not widely used in multi-storey commercial buildings in Australia. However, it is possible to install and use them in office buildings, and there are examples in Sweden and Germany of their use in multi-storey residential buildings and one example in Australia in a two-storey building (the Thurgoona Campus of CharlesSturtUniversity in Albury). The main advantages of composting toilets are that they require little or no water for flushing, thus reducing water demand, and they reduce the quantity and strength of the wastewater to be treated or disposed and return nutrients to the environment (US Environment Protection Agency, 1999).
Waterless toilets operate by collecting wastes in a chamber, where the waste is aerated and mixed. Carbon-rich mulch is also added to assist with the decomposition process. They require significant levels of ongoing maintenance to ensure correct levels of moisture, oxygen, temperature and carbon are maintained for efficient operation.

Vacuum toilets

Vacuum toilets remove waste from the toilet bowl using a vacuum pump. The waste is macerated and either discharged to the sewer or transported to a holding tank or treatment system. These are commonly used in aircraft and marine transportation, and are increasingly being used in commercial and public restrooms. The average amount of water used is between 1 and 1.5 L per flush (Chanan et al., 2003). However, energy use can be expected to be higher than with conventional toilets, as a vacuum system will use in the order of one kWh per 500 flushes, whereas a standard flush system will use the equivalent of 0.8 kWh (Chanan et al., 2003).

Urinals

Low water use urinals
In Australia, men's toilets in public and commercial buildings are typically fitted with a urinal in addition to a standard toilet. Trough or gutter-type urinals in public toilets are often many metres wide, and require large amounts of water and disinfectant chemicals to keep them clean (Savewater, 2006). In some systems, water is applied automatically through a continual drip-feeding system or by automated flushing at a set frequency, 24 hours a day, 7 days a week, regardless of whether or not the urinal has been used. Water consumption varies with the system model, settings and usage rate, from 50 to 100 kL/year (30 to 70 flushes of 4 litres each per day). Cyclic 'fill and dump' units operating on a 24 hours a day, 7 days a week basis can waste over 500 L/year (DEH, 2006a).

Urinals that use lower amounts of water include:

• sensor operated - these detect the presence of people through movement sensors or door switches (combined with an electronic delay to stop flushing for a set period after flushing) (DEH, 2006a)
• single unit systems - these replace trough and gutter systems with single unit systems that have individual flushes (left figure).

Standard trough-type urinals in Australia use an average of 6 litres of water per flush, while water-efficient urinals use 2.8 litres per flush (Chanan et al., 2003). Recent developments at Caroma have resulted in Smart Flush systems using 0.8 litres per flush.

Waterless urinals

Waterless urinals are being used in commercial buildings, hotels and government institutions. They are currently installed in a number of buildings in Australia and more widely around Europe, New Zealand and US. Most of these urinals operate through the use of an oil barrier between the urine and the atmosphere, preventing odours from escaping. The potential water savings from a waterless urinal compared to a 2.8 litre per flush urinal in a commercial building is approximately 1.5 ML/annum, based on typical usage of four flushes per day (DEH, 2006a).
There are two major types of waterless urinals, based on the unit's ability to prevent sewer gases entering the room. The original waterless urinal uses an oil to create a seal between the sewer gases in the sanitary pipe work and the air in the room. Further developments have taken away the need for an oil seal and have replaced the seal with a collapsible silicone tube that closes after fluid has passed through it. This tube is designed to work as a one-way valve to prevent gases attempting to flow from the sanitary pipe work into the room.
Both types of waterless urinals are subject to the build-up of uric salts in the pipe work and traps. Therefore it is important to consider how to manage this build-up so as to maintain health and amenity in the toilets.

Taps

Aerators and flow restrictors
Taps can be replaced with water-efficient taps that have inbuilt aerators and/or flow restrictors. Alternatively, aerators and flow restrictors can be installed in existing tapware to improve efficiency.

Sensor taps
Sensor taps are automatic shut-off taps, such as push-button or lever-operated taps that shut off automatically after a set time to reduce the potential for taps to be left running too long or not turned off (e.g. a 6-star WELS-rated tap has a running time set between 5 to 10 seconds at a flow rate of 4 L/s).

Showers

Water-efficient showerheads
Under the WELS rating scheme, water-efficient showerheads are those that deliver 9 L/s or less. Showers can also be fitted with digital read-out meters that show the user the amount of water being consumed and the duration of the shower. This can encourage shower users in an office building situation to reduce water demand for showers (Chanan et al., 2003).

Sensor-operated and automatic shut-off taps
These can be installed in showers, particularly for high-usage wash rooms.

Coin operated showers
These are often used in caravan parks.

Garden opportunities

Although water use in gardens is typically lower than other end uses in public, commercial or industrial buildings, it is still worth considering the following water-efficient practices where applicable.

• Irrigation systems
• Garden design

Irrigation systems

Soil moisture sensors
Soil moisture sensors detect the amount of moisture in the soil, and suspend irrigation when the soil moisture is at a specified level. Potential for water saving is much higher than rain sensors, as soil moisture sensors detect water directly in the root zone.

Automated centralised watering systems
These sensors save water through ensuring continuity of water application across an area, and can be incorporated with soil moisture and rain sensors.

Drip irrigation/innovation in spray nozzles
These measures provide for more efficiency in water application, as water is not wasted in areas that do not require watering (DEH, 2006a).

Sub-surface irrigation
'Australian studies show that an average of 30% of applied irrigation water passes through the root zone without being used by the crops it is intended to sustain. This water either becomes groundwater recharge or is intercepted by drainage networks and contributes to waterway pollution. Sub-surface drip irrigation has shown great potential for increasing crop yield and uniformity, while decreasing water use and environmental impact. Importantly, sub-surface irrigation applies water directly to the plant's root zone at a rate closely matching that required for optimum plant growth.'(National Program for Sustainable Irrigation, 2005)

Garden design

Water-efficient garden design includes:

• mulch
• planting drought tolerant species
• improving soil.

Water harvesting

• Rainwater
• Capturing rainwater
• Stormwater
• Capturing stormwater

Rainwater

Rainwater is precipitation collected through gutters and downpipes from roof tops or other above ground surfaces. It can be used directly without any treatment for toilet flushing, irrigation and vehicle washing, or with treatment for drinking water, showers and hand basins (DEH, 2006b). Rainwater can also be used as make-up water for cooling towers, which could minimise blowdown, as it has lower levels of total dissolved solids compared to scheme water (Chanan et al., 2003).

In metropolitan areas, rainwater can be used for a number of purposes in residential, commercial and public buildings, generally without other controls being required. These purposes include:

• laundry taps
• clothes washing
• toilet flushing (including urinals)
• garden watering
• swimming pool top-up
• car washing
• fire sprinkler systems
• heating systems
• ornamental water features.

Capturing rainwater

Rainwater can be stored in rainwater tanks above or below ground. Other innovative storage methods include slim-line tanks, storage built into house walls, bladder tanks fitted into the floor of a building, and gutter storage.

Stormwater

Stormwater can be used for irrigation and local wetland charging.

Capturing stormwater

Stormwater can be captured and stored in underground tanks or open water bodies, such as wetlands, lakes and engineered detention basins: 'aquifer storage involves the capture of stormwater in a detention basin, from where it is allowed to either percolate down through the strata to a suitable aquifer or is injected through a recharge well. Groundwater is typically more saline than stormwater, and therefore the stormwater floats on the top of the groundwater' (DEH, 2006a).

The simplest method of using stormwater is diverting rainwater from impervious areas directly onto garden beds: 'large underground modular water tanks (greater than 6,000 litres) are being used in many commercial, residential and public buildings and can be designed to include a filtration unit and tank modules wrapped in geotextile fabric, with a polypropylene plastic liner. Without the impervious plastic liner these systems can be used to facilitate infiltration of stored stormwater run-off into the surrounding earth' (DEH, 2006a).
'Stormwater re-use systems need to ensure that plumbing issues are addressed, particularly backflow prevention, to ensure that no cross-contamination of the reticulated or rainwater supply occurs. Furthermore, a higher level of maintenance and monitoring of the system may be required due to the lower quality of the water that is being used, including screens (to remove litter and debris), first flush pits (to trap sediment), and filters to remove some nutrients/contaminants from the water prior to use. Devices to disinfect the water,