The charts below provide a perspective on fresh water withdrawals across various economic sectors on a global1 and U.S. basis2. 'Agricultural' and 'Power Generation' are the two largest withdrawal segments, together representing about 80 per cent. Agriculture alone accounts for about two-thirds of global withdrawals on a global basis but declines to about 40 per cent 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 per cent 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 per cent of withdrawals.
Even though small overall, the oil and gas industry can still be a material user of water at local levels.
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 per cent 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 pressurising water in the U.S. was approximately 25 per cent more than that used for all residential and commercial lighting.3
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 Although the amount of water consumed or withdrawn varies by plant cooling technology, conversion efficiency and fuel type, it still holds true that the more electricity generated, the higher the water use.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.4