Understanding the relationship between energy and water

Water fundamentals

When taken in total, the volume of fresh water on earth is enough to support the world’s population. But according to the United Nations, while “there is no global water scarcity as such, an increasing number of regions are chronically short of water."¹ Why is this? Part of the reason is uneven resource distributions such as seasonal rainfall patterns impacted by cyclic droughts or floods. Another is growing human demand. Scarcity may also result when water is not supplied adequately to the people who need it. This is often due to human factors such as substandard water treatment and transportation infrastructure, poor water governance, economics, lack of institutional knowledge or adaptive capacity, war, culture, or impacts to water quality.

Since water scarcity may arise at any time from any combination of resource, demand or supply factors, it is difficult to predict when and where it will occur.

Experts point to this complexity as the reason why a given water-management approach that works in one area may not work well in another.² Meeting forecasted growth in global freshwater demand will require local solutions, on both the supply and demand sides. No one solution will fit all needs, but through sharing best practices or technologies, education, infrastructure investments and policies to ensure the right water for the right use, we can begin to address scarcity factors in a region.

Key water terms and definitions

Many definitions, terminology and units have come into use in the field of water management over time. ExxonMobil follows the IPIECA-API-OGP “Oil and Gas Industry Guidance on Voluntary Sustainability Reporting,” 2015 edition and uses the following definitions:

Withdrawal: the volume of fresh water removed from all sources for use by a facility or project

Consumption: the difference between fresh water withdrawn and fresh water returned by a facility or project

Water use: a general, colloquial meaning referring to the removal of water from its natural location or the changing of its qualities as a result of human activity

Fresh water: water with a total dissolved solids (TDS) concentration of less than 2,000 milligrams per liter

Water stress: when the total annual runoff available for human use per capita drops below 1,700 cubic meters per person per year

Scarcity: when the total annual runoff available for human use per capita drops below 1,000 cubic meters per person per year

Download IPIECA 2015 for more terms.

Water and energy

Globally, the oil and gas industry uses far less water than agriculture or power generation, though it can be a significant user of water at the local level. The diagrams below list examples of water use and quality aspects at various stages of the oil and gas value chain.

Freshwater intensity

Freshwater intensity is the total amount of freshwater needed to produce an identical unit of energy, for a variety of energy sources and transportation fuels.

Plant-based ethanol, like most biofuels, requires a significant amount of water for production and processing, with irrigated feedstocks falling at the high end of use. Hydroelectric power plants also require significant amounts of water due to evaporation and subsurface seepage from reservoirs. Electricity generation requires large volumes of water for cooling, although gas-fired turbines are more efficient and require less water than coal-fired plants. Natural gas requires relatively little water to produce. This is true for conventional gas as well as shale or tight gas — the additional water needed during a one-time hydraulic fracturing operation makes little difference over the life of a well and uses thousands of times less water than what would be required to irrigate, harvest and process an equivalent amount of biofuel energy over the same time period. Oil sands and conventional oil are also comparatively light in their water requirements.

Water use across industries

The charts below provide a perspective on fresh water withdrawals across various economic sectors on a global³ and U.S. basis.⁴ ‘Agricultural’ and ‘Power Generation’ are the two largest withdrawal segments, together representing about 80 percent. Agriculture alone accounts for about two-thirds of withdrawals on a global basis but declines to about 40 percent for the U.S. and other developed economies, where the proportion of water used for electrical power generation rises sharply compared to the proportion used for agriculture.

The ‘Industrial’ sector, including the ‘Oil and Gas industry,’ accounts for less than 10 percent of total water withdrawals in even the highest-income countries — far less than the water needs for Agriculture or Power Generation. In the U.S., where more detailed water data is available, we see that the oil and gas sector accounts for around 2 percent of withdrawals.

This highlights another important aspect of water: It is essential in providing energy, just as energy is needed to provide water. This is called the water-energy nexus. For example, in the U.S., about 12 percent of all power generated goes to providing water services (extraction, transportation and treatment). In some states, such as California, this percentage is considerably higher. In 2010, the amount of energy (611 billion kilowatt hours of electricity) used for pumping, treating, heating, cooling and pressurizing water in the U.S. was approximately 25 percent more than that used for all residential and commercial lighting.⁵

Thus, water constraints can become energy constraints, and energy constraints can become water constraints. The relationship is particularly clear in challenging situations such as converting salt water to fresh water through desalination, or pumping water over mountain ranges. Conversely, improvements in energy efficiency can reduce water consumption. Electric power-generating equipment requires enormous amounts of water for cooling. Although the amount of water consumed or withdrawn varies by plant-cooling technology, conversion efficiency and fuel type, it still holds true that the more electricity generated, the higher the water use.

For example, it’s interesting to note that the electricity used in U.S. homes requires about 250 gallons of water per person per day to generate — well over twice the amount of actual water that person consumes in a day.⁶

Sources

1. UNDESA Water for Life Decade. Accessed at http://www.un.org/waterforlifedecade/scarcity.shtml
2. S.Islam, Y.Gao and A.S.Akanda, “Water 2100: A synthesis of natural and societal domains to create actionable knowledge through AquaPedia and water diplomacy,” in Hydrocomplexity: New Tools for Solving Wicked Water Problems, IAHS Publ. 338, 2010.
3. 2000 Freshwater withdrawal data per U.N. World Water Development Report 2014
4. 2005 Freshwater withdrawal data per U.S. Geologic Survey’s Estimated Use of Water in the United States in 2005
5. Sanders and Webber 2012  “Evaluating the energy consumed for water use in the United States,” http://iopscience.iop.org/1748-9326/7/3/034034/pdf/1748-9326_7_3_034034.pdf
6. C. Fishman, "The Big Thirst," Free Press, New York, 2011, p2