According to the U.S. Department of Energy, present day water and energy systems are interdependent. Water is used in all phases of energy production and electricity generation. Energy is required to extract, convey, and deliver water of appropriate quality for diverse human uses, and then again to treat wastewater prior to their return to the environment. Resources available in this sub-theme include reviews of diverse technologies and information on alternative energy sources such as biogas and solar, as well as other energy and water resources.