Abstract

During the Millennium Drought in Australia, a wide range of supply-side and demand-side water management strategies were adopted in major southeast Australian cities. This study undertakes a time-series quantification (2001–2014) and comparative analysis of the energy use of the urban water supply systems and sewage systems in Melbourne and Sydney before, during and after the drought, and evaluates the energy implications of the drought and the implemented strategies. In addition, the energy implications of residential water use in Melbourne are estimated. The research highlights that large-scale adoption of water conservation strategies can have different impacts on energy use in different parts of the urban water cycle. In Melbourne, the per capita water-related energy use reduction in households related to showering and clothes-washing alone (46% reduction, 580 kWhth/p/yr) was far more substantial than that in the water supply system (32% reduction, 18 kWhth/p/yr). This historical case also demonstrates the importance of balancing supply- and demand-side strategies in managing long-term water security and related energy use. The significant energy saving in water supply systems and households from water conservation can offset the additional energy use from operating energy-intensive supply options such as inter-basin water transfers and seawater desalination during dry years.

INTRODUCTION

In recent years, concerns about environmental sustainability, rapidly increasing energy costs and climate change mitigation, together with the increasing uptake of energy-intensive alternative water sources, have driven a growing interest in understanding and managing energy use and greenhouse gas emissions in the urban water cycle.

The Millennium Drought was a prolonged period of dry conditions occurring in much of southern Australia from late-1996 to mid-2010 (Bureau of Meteorology 2015b). In southeast Australia, dry conditions were most profound between 2001 and 2009 (Van Dijk et al. 2013). The region has some of the most populated Australian cities, including Adelaide, Brisbane, Melbourne and Sydney. At the height of the drought, the total water use in the region reduced by over 50% (from the 2001 level) (Australian Bureau of Statistics 2006, 2015a). The agricultural sector was most severely affected, followed by urban water use (i.e. the percentage of water use by the household sector was on average less than 10% of total state-wide water use). The drought led to a series of policy responses from the water sectors. A wide range of supply-side (e.g. inter-basin water transfers, desalination, rainwater harvesting) and demand-side strategies (e.g. water conservation campaigns, water restrictions) were implemented. It is well documented how the region responded to this worst drought on record (Grant et al. 2013; Turner et al. 2016), but relatively little is known about the energy implications of the drought and the implemented water management strategies on the urban water cycles (i.e. water supply systems, sewage systems, residential water end use). In addition, most of the studies in the literature present a ‘snapshot’ analysis of a single year. Studies considering the influence of time on water-related energy use are less evident in the literature (Kenway et al. 2011b). This study therefore aims to fill this gap.

This paper explores the energy implications of the Millennium Drought on the urban water cycles in two southeast Australian cities – Melbourne and Sydney. It quantifies longitudinally the energy use of the water supply systems and the sewage systems in the two cities from 2001 to 2014, and estimates the residential water-related energy use in Melbourne before and after the drought. The energy implications of the drought, and the implemented supply- and demand-side strategies (Table 1) on the water supply systems, sewage systems and residential water end use are then discussed. The major contribution of this work is to provide a case study on analysing the temporal water-related energy impacts of drought on different parts of the urban water cycle.

Table 1

Major supply- and demand-side strategies implemented in Melbourne and Sydney in responses to the Millennium Drought

Supply side Demand side 
Melbourne 
 Building the North-South Pipeline Water restrictions 
 Building the Victorian Desalination Plant Target 155 campaigna 
 Leakage and pressure management Living Victoria Rebate Programb 
 Showerhead Exchange Program 
 waterMAP Programc 
Sydney 
 Operating the Shoalhaven Drought Transfer Scheme Water restrictions 
 Building and operating the Sydney Desalination Plant NSW Home Saver Rebates Programd 
 Leakage and pressure management Business water efficiency programs 
Supply side Demand side 
Melbourne 
 Building the North-South Pipeline Water restrictions 
 Building the Victorian Desalination Plant Target 155 campaigna 
 Leakage and pressure management Living Victoria Rebate Programb 
 Showerhead Exchange Program 
 waterMAP Programc 
Sydney 
 Operating the Shoalhaven Drought Transfer Scheme Water restrictions 
 Building and operating the Sydney Desalination Plant NSW Home Saver Rebates Programd 
 Leakage and pressure management Business water efficiency programs 

aPromoting a voluntary household water use target of 155 L/p/d (Turner et al. 2016).

bProviding rebates for water efficient products such as washing machines, showerheads and dual-flush toilets (Fyfe et al. 2015).

cHigh water use businesses to prepare water efficiency improvement plans (EPA Victoria 2008).

dProviding rebates for water-related products such as water-efficient washing machines, hot water systems and rainwater tanks (Fyfe et al. 2015).

CASE STUDY BACKGROUND

Melbourne (the capital city of the Australian state of Victoria) had 4.5 million residents as of 2015 (Australian Bureau of Statistics 2015b). It obtains water from an interconnected system of 10 storage reservoirs with a total storage capacity of 1,810 GL (Melbourne Water 2013), which is more than three times the total urban water demand in 2001 (500 GL) (Melbourne Water 2014a). The water supply system is mostly gravity fed. During the Millennium Drought, the average inflow into Melbourne's main water supply reservoirs (1997–2009) was only 376 GL/year, compared to the long-term average of 615 GL/year (Melbourne Water 2016). For the sewage system, all sewage was treated to a secondary level before the introduction of tertiary treatment in one of the treatment plants in 2012.

Sydney (the capital city of the Australian state of New South Wales) is the most populous city in Australia (4.9 million as of 2015) (Australian Bureau of Statistics 2015b). Prior to the drought, it already had an inter-basin water transfer pipeline (the Shoalhaven Transfer Scheme) that can transfer water from the Shoalhaven River to Sydney's catchments in dry years. From 1991 to 2012, the total average inflow to major catchments for Sydney was only 673 GL/year, compared to the long-term average of 2,153 GL/year from 1948 to 1990 (Water Services Association of Australia 2013). For the sewage system, 74%, 3% and 23% of sewage were treated to primary level, secondary level and tertiary/advanced level, respectively, in 2014 (Bureau of Meteorology 2015a).

MATERIAL AND METHODS

The time-series (2001–2014) per capita total urban water use, total energy use in the water supply system, total energy use in the sewage system in Melbourne and Sydney were quantified based on the collected and compiled historical data for urban water use, population served by the water utilities, energy use of water supply systems and energy use of sewage systems. The major data sources are the National Performance Reports in Australia (Water Services Association of Australia 2008; National Water Commission 2011; Bureau of Meteorology 2015a) and numerous public reports published by the water utilities in Melbourne (i.e. City West Water, Melbourne Water, South East Water and Yarra Valley Water) and Sydney (i.e. Sydney Catchment Authority and Sydney Water Corporation) (Lam et al. 2017). Most water utilities report their operational energy use or energy intensity annually. A literature review was used to unveil the historical context of the two cities' responses to the drought.

In this work, the energy implications of some of the supply-side strategies (i.e. Shoalhaven Drought Transfer, Sydney Desalination Plant) and demand-side strategies (i.e. collective impact) implemented during the drought were quantified (Table 1). For the energy implications of supply-side strategies, the annual electricity consumption of the two major supply-side strategies in Sydney were obtained from various utility reports and compiled in an earlier work (Lam et al. 2017). For the energy implications of demand-side strategies, estimates were made on the energy saving associated with water demand reduction in Melbourne and Sydney. For each city, the per capita total water use in 2001 was used as the baseline. The energy saving for a specific year was calculated by multiplying the volume of water saved (against the baseline) with the energy intensity for water supply in that year (i.e., energy saving in year x = (per capita water use in year x – per capita water use in 2001) × population in year x × energy intensity for water supply in year x).

Previous works have shown that residential water-related energy use is dominated by hot water use (Kenway et al. 2011a) with showers and clothes washers contributing the dominant fraction in households studied in Melbourne (Binks et al. 2016). Consequently, this work considers the water-related energy use associated with showering and clothes washing to represent residential water-related energy use. Two residential end use studies (Roberts 2005; Athuraliya et al. 2012) conducted by one of the water retailers in Melbourne (i.e. Yarra Valley Water) in 2004 and 2012 were used to estimate the change in residential water-related energy use through the drought (Figure 1). The results are expressed in per capita primary energy equivalent use (kWhth/p/yr) to compare with that of the centralised water systems. It is assumed that three units of kWhth (thermal) is equivalent to one unit of kWhe (electrical) (Gleick & Cooley 2009).

Figure 1

Overview of the quantification of residential water-related energy use.

Figure 1

Overview of the quantification of residential water-related energy use.

RESULTS AND DISCUSSION

Quantification of urban water use and energy use in the centralised water systems

The per capita total urban water use (L/p/d), total energy use in the water supply systems (GWh) and total energy use in the sewage systems (GWh) between 2001 and 2014 for Melbourne and Sydney are shown in Figures 2 and 3 respectively. Some of the key events that possibly had impacts on water use and the energy use of the supply systems are indicated in the figures.

Figure 2

Per capita total urban water use and total energy use of the urban water supply system and sewage system in Melbourne from 2001 to 2014, with key events.

Figure 2

Per capita total urban water use and total energy use of the urban water supply system and sewage system in Melbourne from 2001 to 2014, with key events.

Figure 3

Per capita total urban water use and total energy use of the urban water supply system and sewage system in Sydney from 2001 to 2014, with key events.

Figure 3

Per capita total urban water use and total energy use of the urban water supply system and sewage system in Sydney from 2001 to 2014, with key events.

The results show that there was a significant reduction in urban water use in both Melbourne and Sydney through the drought. On a per capita basis, it reduced by as much as 43% (2011) and 31% (2010) from the levels of 2001 for Melbourne and Sydney, respectively. Even after the drought ended in 2010, there was only a minor ‘rebound’ in water use. The urban water efficiency gained through the drought seems to have been preserved.

The energy use for water supply in both Melbourne and Sydney was greatly influenced by the drought and the implemented supply and demand-side strategies. Before the drought, Melbourne's water supply system (Figure 2) did not have an inter-basin water transfer pipeline as in Sydney, and the energy use for water supply was therefore much more stable compared to that of Sydney during the drought. The only significant increase in the energy use was observed in 2011 when an inter-basin pipeline (i.e. the North-South Pipeline) came online. The pipeline was built in response to the drought, but commissioned after the drought ended. Similar to the new desalination plant (i.e. the Victorian Desalination Plant), it ceased operation shortly after commissioning.

In Sydney, as the Shoalhaven Drought Transfer started operating in 2002 to transfer water from the Shoalhaven River to Sydney's catchments, the energy use of the water supply system rapidly increased (Figure 3). By the time the transfer was at its peak in 2008, the energy use was over three times that of the pre-drought level. As the drought came to an end in 2010, energy use reduced back to a lower level for around two years, before a newly-built seawater desalination plant operated for around two years.

The time-series of energy use in the sewage systems were relatively stable in both cities, in contrast to the energy use in the water supply systems. The drought and the significant urban water demand reduction seem to have little impact on the sewage systems in term of their energy use. The only significant change in energy use was in Melbourne from 2012 to 2014 when one of their major wastewater treatment plants (i.e. the Eastern Treatment Plant) was upgraded to raise the treatment standard both for improving discharge quality and providing non-potable water recycling (Melbourne Water 2014b).

Energy implications of adopted strategies on the centralised water systems

In terms of the energy implications of the supply-side strategies in Melbourne (Figure 2), the two new supply-side options (i.e. the North-South Pipeline and the Victorian Desalination Plant) only came online after the drought ended, and operated for a short period of time. Data are not available for quantifying their energy implications.

In Sydney, the Shoalhaven Drought Transfer consumed 1,616 GWh of electricity in total between 2003 and 2009 (Sydney Catchment Authority 2006, 2010) to provide approximately 30% of the supply to Sydney during the drought (Metropolitan Water Directorate 2014). To put it in perspective, this total energy use was ten times the annual energy use of the water supply system in a normal year (i.e. 161 GWh in 2014). Another key supply-side strategy was the construction and operation of the Sydney Desalination Plant, which used 535 GWh electricity between 2010 and 2012 at an average energy intensity of 3.38 kWh/kL (Sydney Water Corporation 2012; Bureau of Meteorology 2015a).

In terms of the energy implications of the demand-side strategies, it is estimated in this study that from 2001 to 2014, 404 GWh and 1,212 GWh of electricity were saved in the water supply systems in Melbourne and Sydney, respectively, as a result of urban water demand reduction. While the water use reduction can be a result of both active conservation (e.g. imposing water restrictions, promoting water end use efficiency, increasing the use of decentralised sources, managing leakage) and passive conservation (i.e. water use reduction without demand-side strategies), the significant water demand reduction has been mostly attributed to the change in water use behaviour and the increased use of water efficient devices (Grant et al. 2013; Turner et al. 2016). This energy saving can help offset the extra energy use by the supply-side strategies during the drought. This offset has also been observed in the South East Queensland region which experienced the same drought (Lam et al. 2016).

The energy impacts of the drought and the implemented strategies on the sewage systems in both cities were less distinct as the energy use was concurrently influenced by other factors such as upgrading treatment processes. The amount of sewage collected generally reduced as a result of a reduction in water demand. However, because of stormwater infiltration, the amount of sewage collected increased for those years with more urban rainfall.

Quantification of the energy impacts in residential water end use in Melbourne

The residential water-related energy use before and after the drought were estimated to be 1,272 kWhth/p/yr and 692 kWhth/p/yr respectively (46% reduction). This energy use only includes the hot water energy use for taking showers and using clothes washers, which are the top two household water-related energy use activities. The significant reduction can be mainly attributed to the increased uptake of water-efficient shower heads and water efficiency improvement in clothes washers. In the state of Victoria, where Melbourne is situated, the percentage of households with water efficient shower heads increased from 31.7% (2001) to 71.4% (2013) (Australian Bureau of Statistics 2004, 2013). Comparing residential water end use studies in 2004 and 2012, we also found that there was a slight reduction in the average shower time and shower frequency, which also contributed to a reduction in per capita hot water use. For the use of clothes washers, there was an increased percentage of households using cold water over warm/hot water between 2003 and 2012 (Athuraliya et al. 2008; Smart Water Fund 2013). Energy statistics for the state of Victoria show a reduction of per capita primary energy consumption (including conversion loss) by nearly 15% in the residential sector between 2001 and 2014 (Department of Industry and Science 2015). This can be attributed to factors such as improving household energy efficiency, changes in hot water systems and a reduction in hot water use as quantified in this study.

Implications for managing water-related energy use in urban water cycles

During the drought between 2001 and 2009, water-related energy use in the water supply system, sewage system and residential water end use in Melbourne changed by different extents. The results are expressed in per capita primary energy equivalent use (kWhth/p/yr) for comparison (Figure 4).

Figure 4

Per capita primary energy use of the urban water supply system, sewage system and residential water end use in Melbourne before and after the drought.

Figure 4

Per capita primary energy use of the urban water supply system, sewage system and residential water end use in Melbourne before and after the drought.

The change in the per capita water-related energy use in residential water use was far more substantial than that in the water supply system and sewage system. Comparing the pre-drought and post-drought per capita residential water-related energy use reveals a significant reduction of 46% (580 kWhth/p/yr). For the water supply system, per capita energy use reduced by 32% (18 kWhth/p/yr) between 2001 and 2014. For the sewage system, even though the per capita volume of sewage collected reduced through the drought, the per capita energy use increased as a result of raising the treatment standard, as discussed in the earlier section.

Because of the significant difference in the magnitude of water-related energy use between the residential side and water supply system (i.e. as shown in Figure 4 and in the literature (Kenway et al. 2011a)), demand-side strategies that have a strong influence on hot water use can provide far more significant energy saving, especially in the residential sector, to offset the additional energy use for operating energy-intensive supply-side strategies (on top of the supply system energy saving benefits as quantified in the earlier section). This demonstrates the need of balancing supply-side and demand-side strategies in managing long-term water security and water-related energy use.

To put the estimated water-related energy use in perspective (including only urban water supply, urban wastewater treatment and a part of the residential water-related energy use), it is approximately 2% of per capita total primary energy consumption in the state of Victoria (Department of Industry and Science 2015).

CONCLUSIONS

This work provides a rare time-based analysis of water-related energy use of two major cities through a severe drought. It shows how water-related energy use can change rapidly within a decade timeframe. This historical case demonstrates the significant energy impacts of some supply-side strategies (e.g. inter-basin water transfers, seawater desalination) and large-scale adoption of water conservation strategies (e.g. water restrictions, conservation campaigns and rebates, leakage management). The energy impacts experienced by the water supply systems, sewage systems and residential water end use differ considerably both in magnitude and temporal sense. The operating infrastructure for relieving the water shortage resulted in nearly 50% and over 200% increases in the per capita energy use in the water supply systems in Melbourne and Sydney, respectively, during the dry years. In contrast, water demand reduction (mostly as a result of the drought and implemented water conservation strategies) offered significant long-term energy saving in both the water supply systems and residential water end use. This reflects the importance of considering the balance of supply-side and demand-side strategies in managing long-term water security and water-related energy use.

ACKNOWLEDGEMENTS

Steven Kenway acknowledges the support of the Australian Research Council, with DECRA funding DE160101322. The authors also thank all of the reviewers for their constructive comments.

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