Table of Contents
Introduction
Water and energy are deeply connected. Every way of producing energy uses water in some form, and moving and treating water also uses energy. For beginners, it is helpful to understand how different energy technologies affect water quantity and water quality, and how this creates trade offs when choosing energy systems. This chapter focuses on what is specific to water use in energy production, not on wider environmental or life cycle topics that appear in other chapters.
Types Of Water Use
Water use in energy production is usually divided into two basic ideas, withdrawals and consumption. Water withdrawal is the volume of water taken from a source such as a river, lake, aquifer, or sea. Water consumption is the part of that withdrawn water that is not returned to the same source because it evaporates, is built into products, or is discharged elsewhere.
A power plant may withdraw a large amount of water but consume relatively little if the water is returned almost unchanged and at a similar location. Other technologies withdraw and consume almost the same amount of water because most of the water evaporates or is lost. The distinction is important because high withdrawals can affect ecosystems and other users, while high consumption directly reduces the amount of water available.
Some uses are direct, such as cooling water in power stations or water in a hydropower reservoir. Others are indirect, also called virtual water, such as water used to grow biomass feedstocks, mine fuels, or manufacture equipment.
Key distinction:
Water withdrawal ≠ Water consumption.
Consumed water is the portion of withdrawn water that is not returned to the same source and is therefore no longer available for other users.
The Water–Energy Nexus
Because water and energy depend on each other, they form what is often called the water–energy nexus. Generating electricity and fuels needs water. Delivering clean and reliable water supplies needs energy for pumping, treatment, and distribution.
This interdependence means that choices about energy systems can ease or worsen local water stress. A technology that looks attractive from a climate perspective may have significant water implications, especially in dry regions. The reverse is also true. Measures designed to secure water may increase energy use, for example long distance water transfers that require energy intensive pumping.
Understanding water use in energy production is therefore essential when planning energy transitions that are both low carbon and resilient in a warming world.
Water Use In Thermal Power Plants
Thermal power plants burn a fuel or use nuclear reactions to boil water and create steam that drives a turbine. They include coal, oil, gas, nuclear, and some biomass plants. Their water use is dominated by cooling. After steam passes through the turbine it must be condensed back into liquid water so it can be reused in the cycle. Cooling systems carry away the waste heat.
There are three main cooling approaches with very different water footprints. Once through cooling withdraws large volumes of water, usually from a river, the sea, or a lake, passes it through condensers, then discharges it back, typically warmer. Withdrawals are very high, but consumption is low, because most water returns to the source.
Recirculating or wet cooling uses cooling towers. Water circulates through a closed loop, and cooling occurs as a portion of the water evaporates in the tower. This system withdraws far less water than once through cooling but consumes more because evaporated water does not return to the source.
Dry or air cooling replaces most water based cooling with air. Air passes over condenser surfaces to remove heat. This greatly reduces water withdrawal and consumption, but often increases costs, reduces efficiency, and can lower power output on very hot days.
In addition to cooling, water is used within the boiler and steam cycle for make up water, in flue gas cleaning systems, and for other plant processes. These uses are smaller than cooling but can still be important, especially in water scarce regions.
Hydropower And Water Use
Hydropower is often treated as a low water user because it does not usually consume water within the turbine itself. Water passes through the turbine and returns to the river. However, the presence of a reservoir changes the water balance.
Large reservoirs increase evaporation from the water surface. In hot or windy climates this evaporation can be significant and is often considered water consumption. The size of this effect depends strongly on climate and on the design and area of the reservoir. Run of river plants, which have minimal storage, tend to have much lower reservoir evaporation.
Hydropower also alters the timing and patterns of flows downstream. While this is not water consumption in the strict quantitative sense, it has major implications for other water users and for ecosystems. Changes in flow timing can affect irrigation, fisheries, and drinking water supply. These flow management aspects are discussed in more detail in the chapter specific to river ecosystems and flow management.
Water Use In Fossil Fuel And Nuclear Fuel Cycles
Water is not only used inside power plants. It is also used in fuel extraction and processing. For fossil fuels, water is used in mining coal, producing oil and gas, and washing, cleaning, and refining fuels. Some extraction methods, such as hydraulic fracturing, use substantial volumes of water and can affect local aquifers if not managed properly.
The water footprint of fossil fuels depends on geology, extraction methods, and environmental practices. In some regions, oil sands and unconventional gas production have particularly high water use and can lead to contamination issues if wastewater is not properly handled.
Nuclear energy also has upstream water use, mostly in mining and processing uranium and in some types of fuel fabrication. However, in many assessments, the dominant water use for both fossil and nuclear electricity comes from the cooling systems of the power plants rather than from the fuel cycle itself.
Water Use In Bioenergy Systems
Among all major energy pathways, bioenergy is often the most water intensive, primarily because of the water needed to grow biomass. The key distinction is between rain fed and irrigated biomass. Rain fed biomass relies on natural rainfall. Irrigated biomass uses additional water from rivers, aquifers, or reservoirs, which becomes blue water consumption.
Growing energy crops such as sugarcane, corn, or oil crops can involve very large quantities of water per unit of energy produced, especially where irrigation is necessary. This can compete with food production and with environmental water needs. The debate over food, fuel, and land use frequently includes water concerns.
Water is also used in bioenergy processing, for example in fermentation, distillation, and cooling in biofuel refineries, and in cleaning and handling solid biomass. Compared to the water used in the fields, processing water use is usually much smaller but can still matter locally, especially where facilities are concentrated in water stressed regions.
Water Use In Renewable Electricity Technologies
Renewable technologies differ greatly in how much water they use during operation. Wind power uses very little water. Once turbines are built and installed, water use is limited to occasional cleaning and very small amounts for maintenance.
Solar photovoltaic systems also have very low operational water use. The main need is for periodic cleaning of panels to maintain efficiency, especially in dusty regions. The amount of water required depends on cleaning methods, frequency, and whether dry cleaning technologies are used. Concentrated solar power, which appears in a separate chapter, often uses more water because it relies on thermal cycles and may incorporate wet cooling, similar to conventional thermal plants.
Geothermal energy uses water differently depending on the system. High temperature plants that use steam from underground reservoirs may condense and reinject fluids back into the ground. Losses through leakage or venting can lead to some water consumption. In some designs, additional water is injected to maintain reservoir pressure. In low temperature direct use and geothermal heat pumps, water consumption is often relatively low, especially if fluids are circulated in closed loops.
Marine energies like tidal and wave power generally have minimal freshwater use during operation. Most water interaction occurs in the marine environment, and it is the energy of moving water that is used, not the water as a consumable input. However, manufacturing and installation of equipment have upstream water footprints that are captured in broader life cycle assessments.
Water Quality Impacts From Energy Production
Water use is not only about quantities. Energy production can alter water quality through thermal pollution, chemical discharges, and physical changes to water bodies.
Thermal power plants with once through cooling often return water at higher temperatures. Warmer water holds less dissolved oxygen, which can stress or kill aquatic organisms and alter ecosystem composition. Regulations may limit the allowed temperature increase of discharged water to protect ecosystems and other users.
Fuel extraction and processing can release pollutants into water. Examples include acid mine drainage from coal mining, hydrocarbons and drilling chemicals from oil and gas operations, and heavy metals or radionuclides from poorly managed uranium mines. Bioenergy systems can contribute nutrients and agrochemicals to rivers and lakes when fertilizers and pesticides used in fields run off during rainfall.
Hydropower reservoirs can change water quality by altering temperature profiles, oxygen levels, and sediment transport. Water released from deep reservoir layers can be colder and lower in oxygen than natural flows, with effects on downstream ecosystems and sometimes on drinking water treatment requirements. Although the water volume may be similar, its quality can be significantly different.
Water Use Metrics And Comparison
To compare water use across technologies, different metrics are used. A common measure is water use per unit of electricity produced, often written as cubic meters per megawatt hour, $m^3 / MWh$. When focusing on life cycle water use, the unit may be liters per kilowatt hour, $L / kWh$. These metrics can refer specifically to consumption or to withdrawals, so it is important to know which is being reported.
Estimates vary widely depending on location, plant design, cooling technology, and system boundaries. As an illustration, thermal plants with once through cooling typically show high withdrawals but low consumption, while plants with recirculating cooling show lower withdrawals but higher consumption per unit of electricity. Wind and solar photovoltaic tend to be at the low end of operational water consumption, while irrigated bioenergy and some hydropower reservoirs can be much higher.
Important metric:
Water intensity of electricity = $\dfrac{\text{Water use (withdrawal or consumption)}}{\text{Electricity generated}}$
Common units: $m^3 / MWh$ or $L / kWh$.
These comparisons help identify technologies that are more compatible with water stressed regions and allow planners to weigh water and climate considerations together.
Water Constraints Under Climate Change
Climate change alters the availability and variability of water resources. Changing precipitation patterns, more intense droughts, and altered river flows affect both energy demand and energy supply. Thermal power plants may face cooling water shortages or tighter environmental limits on discharge temperatures during heat waves and low flows. Hydropower output can fall during extended droughts and may become more variable from year to year.
In arid and semi arid regions, competition for water between agriculture, cities, ecosystems, and energy production is already intense. As climate change accelerates, energy systems that are heavily dependent on freshwater can become less reliable or more expensive to operate. This makes low water energy options increasingly attractive where feasible.
Energy planners now need to test future energy scenarios against climate driven water constraints. This includes checking whether planned power plants will have access to sufficient cooling water, whether hydropower patterns will match demand, and how energy choices will affect the resilience of water supply systems.
Reducing Water Impacts Of Energy Systems
There are several strategies to reduce the water footprint of energy production. One approach is technological change within power plants. Examples include choosing dry or hybrid cooling systems, improving plant efficiency so less heat needs to be rejected, or using non freshwater sources such as seawater or treated wastewater for cooling where appropriate and environmentally acceptable.
Another approach is changing the energy mix to favor technologies that use less freshwater during operation, for example increasing wind and solar photovoltaic in water stressed regions, or preferring rain fed bioenergy over irrigated crops where bioenergy is needed. Careful siting of projects can also avoid the most water scarce locations and reduce competition with other water users.
Integrated planning across water and energy sectors helps align investments. Instead of planning energy in isolation, authorities can coordinate with water managers to ensure that new power plants, desalination facilities, and irrigation schemes are compatible. This integrated view supports both climate mitigation and adaptation objectives.
Conclusion
Water use in energy production is a central aspect of environmental performance and system resilience. Different technologies interact with water in distinct ways, through withdrawals, consumption, and changes to quality and flow. As climate change increases pressure on water resources, understanding and managing these water energy links becomes critical for choosing sustainable energy pathways that respect both energy security and water security.