Energy and water are both essential to sustainable development and economic productivity. Ample supplies of water are essential to energy production, and water management is dependent on ample supplies of energy for water treatment and transportation. The critical nexus between energy and water has been recognized in a variety of recent studies, but the policy and regulatory machinery that this nexus depends on is not keeping up with the growing challenges.
Population growth and societal demand for improved quality of life will require more clean water for drinking and sanitation, more water for irrigation of crops to feed more people, expanding supplies of affordable and reliable energy to meet basic human needs and to enable substantial growth in industry and commerce. In contrast, the fresh water resources needed for the many aspects of sustainable development are limited and essentially un-expandable.
In future decades, this growing demand for fresh water and increasingly stressed water resources, along with a growing number of users competing for these resources, will lead to water use conflicts. Just as energy is increasingly seen as a national security issue, water resources will increasingly emerge as strategic assets that nations and sub-jurisdictions within nations will compete for and protect.
On both a global and national basis, the largest consumer of water is agriculture. Water taken from fresh water sources for irrigation is effectively lost to other purposes, such as municipal water supplies. Almost 85% of water consumption in the U.S. is dedicated to agriculture. In contrast, even though about 98% of U.S. electricity generation requires water for cooling or for direct use in generation, most of the water withdrawn for electricity production by the typical thermoelectric power plant is returned to the water body from which it was withdrawn, where it can be used again for other purposes. Only 3.3% of water consumption in the U.S. is dedicated to the cooling of thermoelectric power plants (i.e., plants that produce electricity by thermal processes, including nuclear plants, coal plants, and natural gas plants, most of which use steam-driven turbines to generate power). Note that if measured on the less relevant basis of water withdrawal rates instead of water consumption rates, thermoelectric plants take in (and return to the source water body) a much larger percentage of the total available fresh water.
On a gallon per megawatt-hour basis, nuclear energy currently uses slightly more water than comparable fossil-fired plants, in both the once-through cooling mode and the closed-cycle cooling mode. Nuclear energy consumes much more water than some sources of renewable energy, such as wind and photovoltaic solar, but generally less water than other sources of renewable energy, such as geothermal and concentrating solar. Retrofitting of emissions control systems on fossil plants are already increasing their water consumption rates. When fossil plants begin to deploy carbon capture and sequestration to reduce CO2 emissions, their water consumption rates will increase even more, with consumption rates exceeding those of nuclear energy. It is also important to note that most of the emerging technologies being advocated to reduce U.S. reliance on foreign sources of oil and gas (e.g., ethanol, bio-diesel, oil shale, hydrogen) are in fact heavy consumers of water, well in excess of traditional oil and gas production requirements. Clearly, there are no “silver bullets” when it comes to either energy production or water usage.
The U.S. Congress recognized the importance of issues at the nexus of energy and water, and asked the Secretary of Energy in Dec. 2004 for “a report to Congress on the interdependency of energy and water, focusing on the threats to national energy production resulting from limited water supplies...” A similar request was repeated in the Energy Policy Act of 2005. These requests resulted in a December 2006 Report to Congress from DOE entitled “Energy Demands on Water Resources: A Report to Congress on the Interdependency of Energy and Water.” That report discussed a parallel effort to prepare an action plan – an Energy-Water Research and Development (R&D) Roadmap, a draft of which is currently under review at DOE.
Both the U.S. Environmental Protection Agency (EPA) and the U.S. Nuclear Regulatory Commission (NRC) provide regulatory oversight over nuclear plant environmental matters, including water. In addition, state water authorities provide oversight over each power plant within its jurisdiction, via the National Pollutant Discharge Elimination System (NPDES) permitting process managed by the EPA and implemented by delegated states.