With a quarter of the world’s human population already living in regions that suffer from severe water scarcity for at least six months of the year, it is perhaps not surprising that the World Economic Forum recently rated water crises as the largest global risk in terms of potential impacts over the next decade.
Electricity generation is a significant consumer of water: it consumes more than five times as much water globally as domestic uses (drinking, preparing food, bathing, washing clothes and dishes, flushing toilets and the rest) and more than five times as much water globally as industrial production.
While electricity generation consumes far less water than food production globally, it is expected that there will be enormous changes in the water demands of electricity over the course of the 21st century. The International Energy Agency projected a rise of 85% in global water use for energy production between 2012 and 2032 alone.
These changes will be driven by a combination of factors. First, human population growth, which is estimated to rise from 7.4 billion people today to between 9.6 to 12.3 billion by 2100. Second, by improvements in access to energy for the 1.4 billion people who currently have no access to electricity and the billion people who currently only have access to unreliable electricity networks. And third, progressive electrification of transport and heating as part of efforts to reduce dependence on fossil fuels and reduce greenhouse gas emissions.
Exactly how these changes in the water footprint of electricity are going to play out will depend on the national and international energy policies enacted over the next few decades. Historically, energy policies have been influenced by a multitude of factors (national availability of energy resources, financial costs, reliability of supply, security of supply and the like).
Following on from the Paris COP21 agreement, the carbon footprint of energy should have an increased influence on decision making in the sector. As can be seen from Figure 2, there are considerable differences in the lifecycle greenhouse gas emissions from different electricity generation technologies (g CO2eq/kWh), with average values ranging from just 4g CO2eq/kWh for hydropower to 1,001g CO2eq/kWh for coal, though there are significant regional and technological variations in values reported for the same energy source.
While it is important to consider these factors in policy making within the energy sector, it would be a wasted opportunity if policy makers were to overlook the other environmental footprints of electricity generation – and in particular the water footprint – when making decisions on which technologies to support and prioritise. The fairest way to compare electricity sources in terms of their water demand, is to consider their lifecycle water footprint – the consumptive demand of water for construction and operation of the plant, fuel supply, waste disposal and site decommissioning, per unit of net energy produced.
As can be seen from Figure 3, there are staggering differences in the water footprint of different electricity generation technologies. Minimum life cycle consumptive water footprints vary from 0.01 litres per kWh for wind energy, to 1.08 litres per kWh for storage-type hydroelectric power, though there are significant regional and technological variations in values reported for the same energy source.
When these differences between sources are scaled up by the number of units of electricity required to meet the needs of the global population, the implications of the global water footprint of energy generation are phenomenal. Failure to plan and consider the water demands of energy will likely result in insecure and unreliable energy supplies and negative effects on the other important users of freshwater.
We have recently observed the impacts of droughts on US energy supplies from thermoelectric plants and hydropower plants. If policy makers fail to take into account the links between energy and water, we may come to a point in many parts of the world where it is water availability that is the main determinant of the energy sources available for use.
This will inevitably force countries to make emergency decisions on the distribution of scarce water between generating electricity or producing food, maintaining health and sanitation, maintaining industrial production, and/or conserving nature.