MOLLY A. WALTON
More than 2.1 billion people drink contaminated water. More than half the global population – about 4.5 billion people – lack access to proper sanitation services. More than a third of the global population is affected by water scarcity, and 80% of wastewater is discharged untreated, adding to already problematic levels of water pollution. It is clear that the world has a water problem – but energy can be a part of the solution.
Source: ©Bartosz Hadyniak - istockphoto.com
'It is clear that the world has a water problem – but energy can be a part of the solution'
Energy is essential to water supply, to move water to where it is needed and to collect and treat water and wastewater. Water is required for almost all aspects of energy supply, from electricity generation to oil supply and biofuels cultivation. This interdependency  has been a focus of analysis at the International Energy Agency, and the World Energy Outlook (WEO)  found that, on aggregate, energy consumption in the water sector globally is roughly equal to that of Australia today, mostly in the form of electricity, but also diesel used for irrigation pumps and gas in desalination plants. Our analysis also found that the energy sector  accounts for roughly 10% of total water withdrawals and 3% of total water consumption worldwide.
With both water and energy needs set to increase, these linkages will intensify going forward. Our analysis found that the amount of energy used in the water sector is projected to more than double by 2040, while the amount of water consumed in the energy sector (i.e. withdrawn but not returned to source) could rise by almost 60% over the same period.
What then might be the impact on energy demand of achieving Sustainable Development Goal (SDG) 6 (providing clean drinking water and sanitation for all) , and what impact might the water-energy nexus have on the attainment of other United Nations SDGs? The answers to these questions will depend on how this nexus is managed.
Advancements in technology offer new options for managing potential strains on energy and water and could allow countries to leapfrog in terms of the solutions used to achieve SDG 6. For example, building new wastewater capacity that capitalises on the energy efficiency and energy recovery  opportunities being pioneered by utilities in the European Union and the United States could help temper the associated rise in energy demand from providing sanitation for all and reducing the amount of untreated wastewater . In some cases, achieving these targets could even produce energy: WEO analysis found that utilising the energy embedded in wastewater alone could meet more than half of the electricity required globally for wastewater treatment.
There is significant scope to use water more efficiently in the energy sector . The availability of water is an increasingly important measure for assessing the physical, economic and environmental viability of energy projects. Improving the efficiency of the power plant fleet, deploying more advanced cooling systems for thermal generation and making greater use of alternative water sources and water recycling can all help the energy sector lower its water use.
'The availability of water is an increasingly important measure for assessing the physical, economic and environmental viability of energy projects'
Beyond SDG 6, the achievement of other energyrelated SDGs, including taking urgent action on climate change (SDG 13) and providing energy for all (SDG 7) , will depend on understanding the integrated nature of water and energy.
The more a decarbonisation pathway relies on biofuels production, the deployment of concentrating solar power, carbon capture or nuclear power, the more water it consumes. If not properly managed, this means that a lower carbon pathway could exacerbate water stress or be limited by it.
There is also a significant overlap between those who lack access to energy and those who lack access to water. WEO analysis  has shown that decentralised renewable systems (off-grid and mini-grids) are the lowest cost option for providing a majority of the new rural connections needed to achieve SDG 7.1.1 (electricity for all). Pairing these systems with filtration technologies or water pumps can provide access to both electricity and safe drinking water . Similarly, linking a toilet with an anaerobic digester can produce biogas which can help achieve SDG 7.1.2 (clean cooking for all).
It is evident that understanding and accounting for the water-energy nexus is important for the achievement of the SDGs. This is why the IEA’s Sustainable Development Scenario , which presents an integrated approach to achieving the main energy-related SDG targets on climate change, air quality and access to modern energy, will add a water dimension this year. Understanding the implications for the energy sector of ensuring clean water and sanitation for all will provide policymakers with a clearer picture of what they need to do to hit multiple goals with an integrated and coherent policy approach.
Note: The WEO’s work on water as part of the Sustainable Development Scenario will be part of WEO-2018, to be released on 13 November, 2018.
 WEO-2016 Special Report: Water-Energy Nexus, International Energy Agency (IEA). 2016.
 Excluding hydropower which returns much of the water it withdraws to the river; however its water consumption is highly site-specific and the measurement methodology is not yet agreed upon.
 Target 6.2— universal access to sanitation and Target 6.3- halving amount of untreated wastewater released
 Target 6.4—increasing water-use efficiency across all sectors
 WEO-2017 Special Report: Energy Access Outlook, International Energy Agency (IEA). 2017.
 Target 6.1—clean drinking water for all