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US. GIoball CI °Harm^ esear,::h lPirogirarn <br />Global Climate Change Impacts in the United States <br />Water and energy are tightly interconnected; water systems use large <br />amounts of energy, and energy systems use large amounts of water. <br />Both are expected to be under increasing pressure in the future <br />and both will be affected by a changing climate. In the energy sector, <br />i <br />water is used directly for hydropower, and cooling water is critical for ;ice <br />nearly all other forms of electrical power generation. Withdrawals , <br />�an, <br />of freshwater used to cool power plants that use heat to generate <br />electricity are very large, nearly equaling the water withdrawn for - <br />AiKr, v irrigation. Water consumption by power plants is about 20 percent of Oa <br />all non - agricultural uses, or half that of all domestic use.' 97 <br />In the water sector, two very unusual attributes of water, significant weight due to its relatively <br />high density, and high heat capacity, make water use energy intensive. Large amounts of energy <br />are needed for pumping, heating, and treating drinking water and wastewater. Water supply and <br />treatment consumes roughly 4 percent of the nation's power supply, and electricity accounts for <br />about 75 percent of the cost of municipal water processing and transport. In California, 30 percent <br />of all non -power plant natural gas is used for water - related activities.198,'99 The energy required <br />to provide water depends on its source (groundwater, surface water, desalinated water, treated <br />wastewater, or recycled water), the distance the water is conveyed, the amount of water moved, and <br />the local topography. Surface water often requires more treatment than groundwater. Desalination <br />requires large amounts of energy to produce freshwater. Treated wastewater and recycled water <br />(used primarily for agriculture and industry) require energy for treatment, but little energy for supply <br />and conveyance. Conserving water has the dual benefit of conserving energy and potentially reducing <br />greenhouse gas emissions if fossil fuels are the predominant source of that energy. <br />Water and energy are intimately connected. Water is used by the power generation sector for cooling, and energy is used <br />by the water sector for pumping, drinking water treatment, and wastewater treatment. Without energy, there would be <br />limited water distribution, and without water, there would be limited energy production. <br />52 <br />