Can we ensure a sustainable energy and water future?
The trade-offs between energy and water have been gaining international attention in recent years, as resource demand grows and governments struggle to ensure a reliable supply. Significant amounts of water are needed in almost all energy generation processes, from generating hydropower, to cooling and other purposes in thermal power plants, to extracting and processing fuels. Conversely, the water sector needs energy to extract, treat and transport water. Both energy and water are used in the production of crops, including those used to produce biofuels. This relationship is what is known as the water-energy nexus.
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Despite such resource interdependencies, energy planners and governments often make decisions without accounting for existing and future water constraints, and vice versa. It is important to analyse and understand the trade-offs as we move towards the achievement of the Sustainable Development Goals (SDGs) , to avoid incoherent policies and strategies across sectors. For example, biofuels might be an effective way of reducing greenhouse gas (GHG) emissions in the transport sector, however, if the biofuels are irrigated, it may add to water scarcity and cause water demand conflicts by competing with food production for water and land. We need to leverage synergies and foster integrated solutions to ensure that the achievement of one SDG does not hinder the achievement of another.
Trade-offs of the water-energy nexus
Given that almost all energy generation processes require water, its availability is a necessary condition for reaching universal energy access worldwide. At the same time, universal energy access can contribute to better water access (by facilitating water extraction, treatment, and delivery) and water security . Whereas insufficient or intermittent electricity access can limit water availability by restricting pumping, treatment, and distribution, reliable and affordable access can ensure a continuous supply of the required quantities of safe water as well as wastewater treatment services. Improved energy access can also support the use of energy-intensive technologies such as desalination and more powerful groundwater pumps, which is expected to expand rapidly as easily accessible freshwater resources are depleted. However, unless renewable energy is used, these energy-intensive technologies would increase the energy needs and GHG emissions of the water sector. Moreover, if energy resources are developed without monitoring pollution or taking into account water needs, energy access can have a negative impact on water resources. The energy sector not only withdraws and consumes water – thus altering water flow patterns and limiting the water available for other users – it also generates large amounts of wastewater that can pollute water resources if not managed properly.
On the other hand, water-related risks can affect the energy sector and slow or hinder progress towards universal energy access. Opportunities for power generation or energy extraction might be constrained by changing water supply patterns due to increased floods and droughts, by reallocation of water resources into other sectors, or by new regulations. We have already seen examples of water shortages shutting down thermal power plants in India and decreasing energy production in power plants in the United States . Climate change is further intensifying energy insecurity, with changing rainfall and surface runoff averages, increased water temperatures, and increased probability of extreme weather conditions. For example, a study  found that in Europe, where thermal power plants account for 78% of the electricity produced and 43% of total freshwater withdrawals, power plants’ capacity could decrease from between 6.3% to 19% during the summer (depending on the cooling system type and climate scenario for 2031–2060).
The way forward
Sustainable energy planning should take into account its water use and needs. Results from the World Bank’s Thirsty Energy initiative show that accounting for the regional variability of water supply and the associated costs of water supply infrastructure for energy can significantly impact energy planning, especially in a water-scarce country like South Africa. The work highlights the importance of the spatial component of energy and water resources and its potential impact on the overall cost of different energy technologies. The results also show that specific energy sector policies can have significant implications for new investments in water supply infrastructure and, in some cases, can strand water supply investments (and vice versa). However, if decision makers plan in a more integrated manner, they can ensure the robustness of water supply for energy and for other water users, thus maximizing the value of both energy and water infrastructure investments.
Win-win solutions are possible. As shown in the Thirsty Energy reports , if water needs and water supply costs are taken into account, energy policies to mitigate climate change impacts could reduce both CO2 emissions and water use by the energy sector. Investing now in renewables such as solar PV and wind, that require little or no water to generate electricity, can help not only to mitigate but also to help adapt to climate change in the future. Besides weighing energy sources, policymakers should also focus on boosting energy efficiency both in the supply and demand side, which also results in lower GHG emissions and water use .
Infrastructure investments made today are therefore critical. Choices and decisions matter about which energy extraction facilities to develop and where, which power plants to build, which to retire, and which energy or cooling technologies to deploy and develop. Energy infrastructure is designed to last for decades and thus, when decisions are made, future water availability should be taken into account, including climate change impacts and future competing water demands across sectors.
In summary, decisions in one sector can have unintended consequences in another, and integrated solutions are crucial to ensure a more sustainable future for all. Understanding the water-energy interrelationship is critical to building more resilient and sustainable energy and water systems.
 For a further discussion on the topic, check the subsection on ‘Energy and Water’ of chapter 6 ‘Cross-cutting issues of energy: Exploring the nexus of water, food, health, and gender’ of the report ‘Sustainable Energy for All 2015—Progress Toward Sustainable Energy’, International Energy Agency (IEA) and the World Bank, 2015.
 See Thirsty Energy infographic: http://www.worldbank.org/en/news/feature/2014/01/16/infographic-thirsty-energy-energy-andwater-interdependence
 van Vliet, et al, 2012. Vulnerability of US and European electricity supply to climate change. Nature Climate Change. p. 1546
 For a further discussion check the Special Feature on ‘Energy Access and the Energy-Water Nexus’ of the Sustainable Energy Access Report, ESMAP, The World Bank Group.