The water-energy nexus – a toolkit for innovation

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Laurent Bellet, Corinne Trommsdorff and Alex Alix, editors of a new book aiming to help the water sector reduce its emissions of greenhouse gases, describe the complexities of the task ahead and challenge water professionals and consumers to look for inspired solutions.

The global demand for energy and water is intensifying because of a growing world population, better standards of living in developing countries, and significant industrial growth in countries such as China and India. Water is used in energy production and supply and, in turn, energy is used for pumping, moving, and treating water. As a result, the links between energy and water systems, in the context of climate change, have grown more complex.

Energy must be viewed as a complex and vulnerable aspect of the water system and vice versa – enter the ‘water-energy nexus’.

This intrinsic relationship between water and energy raises challenging questions for water professionals tasked with reducing carbon emissions. A new book published by IWA Publishing, titled Reducing the Greenhouse Gas Emissions of Water and Sanitation Services: Overview of emissions and their potential reduction illustrated by utility know-how, aims to find answers to address the pressures that climate change is imposing on the global water and sanitation sector.

The water requirements of the energy sector are well documented, whereas data on the energy and associated carbon footprint of the water sector is less readily available. The water and energy crisis faced by most countries in 2022 dramatically demonstrated the vital importance of saving resources, while reducing greenhouse gas (GHG) emissions. Indeed, an increasing number of regions and cities in both the Southern and the Northern Hemisphere are experiencing chronic water stress. California, for instance, has been experiencing a megadrought for years now, and China, India, most European countries, and many others have faced unprecedented droughts. A number of cities have reached ‘day zero’ during summer conditions – the term used to describe the extreme circumstances when a city has used all water available from local resources.

Damage limitation

Climate change will make these situations occur with increasing frequency, as evidenced in the map of water stress drawn up by the World Resources Institute (WRI). According to the new report by the United Nations Convention to Combat Desertification (UNCCD), Drought by Numbers, the number and length of extreme water shortages worldwide have risen by almost a third in just 20 years. More than 2.3 billion people are facing water stress, and it is estimated that in just eight years’ time 700 million people will be at risk of having to leave their home regions to find water.

Climate change impacts water resources particularly and it is still difficult to measure what impact exceeding the limits for global temperature rise may have. Water is one of the main indicators of climate change and changes in water regimes will require many adaptation measures for all sectors that depend on water resources.

The scientific evidence contained in the three parts of the 6th Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) is another reminder of the urgent need to respect the 2015 Paris Agreement. This saw 195 countries agree to the goal of limiting long-term global temperature increases to ‘well below 2°C’ compared with pre-industrial levels and to pursue efforts to limit the increase to 1.5°C by massively reducing their emissions of carbon dioxide and other GHGs.

All sectors of society are affected by the need to decrease GHG emissions. It is estimated that emissions by water and sanitation services represent 3-7% of cities’ GHG emissions. As a comparison, the aviation sector is responsible for 2-3% of global GHG emissions.

Emissions from the water sector result as much from the non-treatment of wastewater and the pollution of aquifers in less developed countries as from the operation of treatment plants. One characteristic of water and sanitation services is that they are interconnected with many other sectors, including energy, agriculture, goods and services production, and waste. As a result, the GHG emissions of water and sanitation services may affect, or be affected by, impacts from these other sectors. For example, after heavy rainfalls, waste accumulating in streets may clog collection networks, causing floods, and this requires additional energy to be used to clean the affected rainwater collection networks and to treat the waste and pollution thus generated. This indirectly increases the GHG emissions of sanitation services.

Opportunities for progress

To address this, the IPCC suggests mitigation possibilities, such as converting wastewater into energy and reducing the consumption of water and energy.

The French Water Partnership (FWP) has gathered in this new book from IWA Publishing an inventory of such solutions implemented by French operators. Members of IWA’s Climate Smart Utilities (CSU) Community of Practice have contributed to this book as reviewers, with the aim of supporting urban water utilities on their journey to adapt, mitigate, and be climate leaders.

Achieving sufficient amounts of good quality water for users relies not only on good management of water resources, but also on technologies, such as desalination, which require significant additional energy. To reach the Sustainable Development Goals, we must explore ways to reduce our pressure on natural resources by improving the efficiency of production processes. All this despite the increasing needs that come with population growth.

The treatment and transportation of drinking water and wastewater represents 1-18% of electricity consumption in urban areas. The water sector can contribute significantly to reducing GHG emissions from energy, and from the direct and indirect emissions associated with service delivery activities.

Following an overview of the origin of emissions within water and sanitation systems, the book presents a review of proven measures to reduce GHG emissions that can be structured around the following three pillars:

  • Implementing lean and efficient approaches: reducing leaks, saving water and energy
  • Embracing the circular economy: recycling wastewater and producing energy on site
  • Decisions and strategies to support the transition to carbon neutrality: purchasing green energy and low carbon supplies, training, awareness, and adapted governance structures

Behaviours of water users

These solutions are illustrated with concrete examples implemented by and for local authorities. It is important to note that in addition to solutions implemented by water services, consumers can play their part in reducing emissions associated with the urban water cycle by reducing both their consumption of water and the heating of that water. Significant progress in housing and the design of appliances have resulted in reduced household water needs. Consumers can also have an impact on the energy needs of wastewater treatment by gaining a better understanding of what belongs in the wastewater system, in particular with regards to micropollutants.

The book aims to provide an overview of possible levers to reduce the GHG emissions of water and sanitation services and provide an analysis of how adaptation measures can embrace this approach.

In France, we have observed that drinking water needs have stabilised over the past three decades although population has increased, and household services have improved. This goes to show how useful it is to optimise all aspects that can improve service efficiency, including GHG emissions.

As services now focus on adapting to the impacts of climate change, the opportunity to also reduce GHG emissions needs to be at the forefront of our minds to ensure we play our part and inspire others to make progress on the journey to carbon neutrality.

The solutions illustrated in this book are each specific to their context and are intended as an inspiration for the readers to rethink solutions. It provides a toolkit that we hope will be useful in both urban and rural environments for local officials and those in charge of designing and managing water and sanitation services.

More information

Reducing the Greenhouse Gas Emissions of Water and Sanitation Services: Overview of emissions and their potential reduction illustrated by utility know-how
Alexandre Alix, Laurent Bellet, Corinne Trommsdorff and Iris Audureau (Eds)
IWA Publishing
Available as an Open Access ebook

WRI map of water stress is available at:

The UNCCD report, ‘Drought by numbers’ is available at:

The editors

Laurent Bellet is water & energy advisor at EDF, Corinne Trommsdorff is chief executive officer and founder of Water Cities, and Alex Alix is programme officer, water & climate, at PFE.