Energy for water: A UK perspective

December 14th, 2015

Iliana Cardenes, University of Oxford, UK

The supply of energy and water are fundamental global issues, yet are often considered in isolation. In recent years, an appreciation of the increasing interdependencies between energy and water has developed. From the growing uptake of desalination and water recycling to deal with water scarcity, to the increase in hydropower plants to meet our expanding energy demands, it is clear that the need to understand the complex relationship between water and energy is becoming much more important.

This short article showcases some preliminary results on the energy requirements for water delivery in a large urban area: London and the surrounding region in England. It is part of a wider study with Thames Water to better understand the energy-water nexus in the context of delivering water services. Thames Water, a water and wastewater utility in the South East of England, operates over 100 water treatment works, 30 raw water reservoirs, approximately 288 pumping stations and 235 clean water service reservoirs1. These Thames Region water systems serve approximately 10 million customers. The article introduces the context of the study, followed by a quantification of energy use and potential reasons for observed trends, and finishes with a short conclusion.

Complex issue

Large quantities of energy are needed to extract, pump, treat and manage water and wastewater, with the total energy consumed for these operations rising globally2. It is an unavoidable fact that water is heavy and requires significant energy to distribute it. Therefore, to manage the energy associated with this activity, a multi-dimensional approach of energy efficiency/avoidance, substitution with renewable energy, and a reduction in the per capita consumption of customers will be required.

This challenge is intensified when combined with population growth and climate change. According to the United Nations3,4 approximately 8% of global energy supply is currently used to deliver water. Estimates for this figure, however, vary greatly from study to study, as well as region to region5,6. These variations are not only dependent on location; regulation; geography; climate; availability of water; quality of water; and treatment, re-use and disposal of sewage; but also on the use of different conceptual boundaries, system definitions, availability of data and stages of the system included7,8.

While there are some studies in the field, we would undoubtedly benefit from more detailed studies in energy and water, with specific conceptual boundaries9. In Nature Climate Change, Rothausen and Conway10 call for more holistic studies investigating energy consumption in water use. They emphasise that to date, the literature has mostly been dominated by non-academic studies. Furthermore, given the lack of quantitative data available for such studies to date, there is a clear opportunity to engage with the water and sewerage sectors to understand how energy is used in water, as this is key to understanding the wider relationship, as well as pressures and opportunities.

Study

Researchers at the Environmental Change Institute, University of Oxford are working in collaboration with Thames Water on the relationship between energy and water. Using illustrative data from the Thames Region in the South East of England, we are evaluating the energy use of water supply and wastewater treatment within the given region, although this article focuses solely on some of the preliminary water treatment results.

Through combining a top-down sectorial assessment of energy use with the bottom-up allocation of energy for water on a physical asset basis, this study is providing a systems-level view of the energy consumption of water. This research is carried out through the integration of detailed data from actual operational infrastructure in the Thames Region, to produce a better understanding of energy use within the territory of a large-scale urban water provider.

Thus, the first aim is to better understand and quantify the energy consumption of the water sector, illustrated through a large water company, in order to enhance our understanding of the energy inputs required for water services from a systems-wide perspective. Figure 1 shows an initial analysis of the average Energy Consumption (units of energy, in kWh, used per unit of water, in m3) of Thames Water’s Treatment Works (representative sample of 73 works) over a period of approximately 5 years. It suggests that water treatment may be becoming more energy efficient. This downward trend suggests that there could be an influence from technological advances.

At the same time, and equally as importantly, the study explores how and why energy consumption is changing, in order to recognise the potential to make realistic reductions. To date, this study has found that large variations in the energy intensity of potable water are dependent on region, season, technology used and asset size amongst other factors.

For example, Figure 2 shows the average energy (kWh) consumed by the water treatment works in the study region. On top of the clear downward trend in energy use per unit of water treated mentioned above, there is a variation in the monthly Energy Consumption (EC) of treatment. This suggests a seasonal influence on energy consumption. As can be seen, there is a distinct spike in energy consumption around each winter (see vertical dotted lines, which are placed on each month of December and peaks 1, 3, 5, 6 and 9).

We would normally expect higher energy consumption in the summer for example due to higher demand for water (peaks 2, 4, 7, 8 and 10)11,12. As such, there might be other factors at play influencing the second peak in energy consumption in the winter, most likely cold winter temperatures leading to increased leakage and burst pipes, pushing up consumption of energy for treatment and distribution.

This study is focusing on a system servicing over 10 million customers, and is already providing us with significant advancements in the understanding and mapping of energy use in large scale water systems. However, understanding how energy is being used is not enough. The next step is to explore the potential for more efficient and sustainable ways of delivering water in the UK.

As such, the study is investigating different technological options available in order to increase the efficiency of the system. In addition, the study focuses on assessing the potential for strategic and planning options to avoid water and energy-intense assets and solutions in the short- and long-term; taking into account increasing water scarcity risks, the effects of climate change, the increase in intense rainfall events, and changing demand. In turn, this will enable us to understand and design more integrated, targeted efforts to conserve water and energy resources which would help deliver a more sustainable future.

Conclusions

It is hoped that the development of this study will help inform the wider global water sector as they develop medium and long-term water and energy use management plans. We have established that energy use across a large sample of assets has reduced over the past 5 years by approximately 10%. There is also a clear seasonality in the energy use of water treatment, with energy intensity often having a peak both in winter and in the summer. Given the current gaps in both academic and industrial literature as well as collaborative policy, more integrated policy making can be sought in partnership with the water sector to help to avoid some of the trade-offs that may occur from lack of clarity and communication.

Together, increasing water scarcity, climate change, increase in intense rainfall events, water pollution, population growth, regulation and changing demand will all have an effect on our ability to supply clean water, and in turn, the energy demands of this delivery. Furthermore, EU Water Framework Directive requirements as well as potential competition between the energy and water sectors and wider society for water will add complexity to the issue.

Forward planning will also have to take existing assets into account, framing nearer term thinking to inform how to move from today’s infrastructure to tomorrow’s delivery of water services. It is imperative to identify the most flexible and strategic options to avoid intense water and energy assets in the short- and long-term, including energy substitution. In order to do this, a comprehensive, systems-level understanding on how energy and water relate, and why this relationship is changing is a crucial step.

References :

Thames Water. Thames Water Water Resources Management Plan 2015 – 2040. (2014). Ofwat. Playing our part – reducing greenhouse gas emissions in the water and sewerage sectors. (2010). UN Water. Partnerships for improving water and energy access, efficiency and sustainability. (2014). UNESCO. The United Nations World Water Development Report 2014: Water and Energy. Paris, UNESCO (2014). Hendrickson, T. P. & Horvath, A. A perspective on cost-effectiveness of greenhouse gas reduction solutions in water distribution systems. Environ. Res. Lett. 9, 024017 (2014). Olsson, G. Water and Energy: Threats and Opportunities. (IWA Publishing, 2012). Spang, E. S. & Loge, F. J. A High-Resolution Approach to Mapping Energy Flows through Water Infrastructure Systems. J. Ind. Ecol. 00, (2015). Zhou, Y., Zhang, B., Wang, H. & Bi, J. Drops of Energy: Conserving Urban Water to Reduce Greenhouse Gas Emissions. Environ. Sci. Technol. 47, 10753-10761 (2013). Yang, J. & Yamazaki, A. Water and Energy Nexus?: A Literature Review. Water West, Stanford Univ. 1-146 (2013). Rothausen, S. & Conway, D. Greenhouse-gas emissions from energy use in the water sector. Nat. Clim. Chang. 1, 210-219 (2011). Environment Agency. Greenhouse gas emissions of water supply and demand management options. (2008). Ainger, C. et al. A Low Carbon Water Industry in 2050 (EA Report: SC070010/R3). Environment Agency (2009).

Iliana is a doctoral student at the University of Oxford’s Environmental Change Institute, working with Professor Jim Hall and Dr Nick Eyre on quantifying the energy consumption of water infrastructure and the water-use cycle. The project evaluates technological options and appraises possible water supply and demand futures, in the context of climate change and policy integration. Her research is supported by Thames Water and a full scholarship from the ‘La Caixa’ Spain Foundation. The article, and the wider research project, have benefited from comments and support from Keith Colquhoun (Thames Water), whose help is gratefully acknowledged. Iliana can be contacted on: iliana.cardenes@ouce.ox.ac.uk.

T: @ilianacardenes W: http://www.geog.ox.ac.uk/graduate/research/icardenestrujillo.html

The views expressed in this article belong to the individual authors and do not represent the views of the Global Water Forum, the UNESCO Chair in Water Economics and Transboundary Water Governance, UNESCO, the Australian National University, or any of the institutions to which the authors are associated. Please see the Global Water Forum terms and conditions here.