Power plant developers consider many factors when determining where to locate a power plant, including the availability of fuel, water, and land; access to electrical transmission lines; electricity demand; and potential environmental issues. Often, developers will consider several sites that meet their minimum requirements, but narrow their selection based on economic considerations such as the cost of accessing fuel, water, or transmission lines, or the costs of addressing environmental factors at each specific site. One key requirement for thermoelectric power plants is access to water. Thermoelectric power plants use a heat source to make steam, which is used to turn a turbine connected to a generator that makes electricity. As shown in figure 1, the water used to make steam (boiler water) circulates in a closed loop. This means the same water used to make steam is also converted back to liquid water —referred to as condensing—in a device called a condenser and, finally, moved back to the heat source to again make steam. In typical thermoelectric plants, water from a separate source, known as cooling water, flows through the condenser to cool and condense the steam in the closed loop after it has turned the turbine. Consideration of water availability during the power plant siting process can pose different challenges in different parts of the country because precipitation and, relatedly, water availability varies substantially across the United States. Figure 2 shows the total amount of freshwater withdrawn in the United States as a percentage of available precipitation. Areas where the percentage is greater than 100—where more water is withdrawn than locally renewed through precipitation—are indicative of basins using other water sources transported by natural rivers and manmade flow structures, or may indicate unsustainable groundwater use. Power plants can use various types of water for cooling—such as freshwater or saline water—and different water sources, including surface water, groundwater, and alternative water sources. An example of alternative water sources is reclaimed water such as treated effluent from sewage treatment plants. To make siting decisions, power plant developers typically consider the water sources that are available and lea costly to use. Fresh surface water is the most common water source for power plants nationally, as shown in table 1. Power plant developers must also consider what cooling technologies they plan to use in the plant. There are four general types of cooling technologies. Traditional cooling technologies that have been used for decades include once-through and wet recirculating cooling systems. Advanced cooling technologies that have focused on reducing the amount of cooling water used are relatively newer in the United States and include dry cooling and hybrid cooling. Specifically: Once-through cooling systems. In once-through cooling systems, large amounts of cooling water are withdrawn from a water body such as a la river, or ocean, and used in the cooling loop. As shown in figure 3, the cooling water passes through the tubes of a condenser. As steam in the boiler water loop exits the turbine, it passes over the condenser tubes. This contact with the condenser tubes cools and condenses the steam back into boiler water for reuse. After the cooling water passes through the condenser tubes, it is discharged back into the water body warmer than it was when it was withdrawn. Once-through cooling systems withdraw a significant amount of water but directly consume almost no water. However, because the water discharged back into the wate warmer, experts believe that once-through systems may increase evaporation from the receiving water body. Furthermore, because of r body is concerns about the harm withdrawal for once-through systems can have on aquatic life—when aquatic organisms are pulled into cooling systems, trapped against water intake screens, or their habitat is adversely affected by warm water discharges—these systems are rarely installed at new plants. Although a number of federal agencies collect data on water, two collect key data that are used to analyze the impacts of thermoelectric power plants and water availability: USGS and EIA. USGS’s mission is to provide reliable scientific information to manage water, energy and other resources, among other things. USGS collects surface water and groundwater availability data through a national network of stream gauges and groundwater monitoring stations. USGS currently monitors surface and groundwater availability with approximately 7,500 streamflow gauges and 22,000 groundwater monitoring stations located throughout the United States. USGS compiles data and distributes a report every 5 years on national water use that describes how various sectors, such as irrigation, mining, and thermoelectric power plants, use water. USGS data related to thermoelectric power plants include (1) water withdrawal data at the state and county level organized by cooling technology—once-through and wet recirculating; (2) water source—surface or groundwater; and (3) whether water used was fresh or saline. USGS compiles water use data from multiple sources, including state water regulatory officials, power plant operators, and EIA. If data are not available for a particular state or use, USGS makes estimates. EIA’s mission is to provide policy-neutral data, forecasts, and analyses to promote sound policy making, efficient markets, and public understanding regarding energy and its interaction with the economy and the environment. In carrying out this mission, EIA collects a variety of energy and electricity data nationwide, about topics such as energy supply and demand. For certain plants producing 100 megawatts or more of electricity, EIA collects data on water withdrawals, consumption, discharge, as well as some information on water source and cooling technology type. EIA annually collects water use data directly from power plants by using a survey. The variety of state water laws relating to the allocation and use of surface water can generally be traced to two basic doctrines the riparian doctrine, often used in the eastern United States, and the prior appropriation doctrine, often used in the western United States. Under the riparian doctrine, water rights are linked to land ownership— owners of land bordering a waterway have a right to use the water that flows past the land for any reasonable purpose. In general, water rights in riparian states may not be bought or sold. Landowners may, at any time, use water flowing past the land, even if they have never done so before. All landowners have an equal right to use the water, and no one gains a greater right through prior use. In some riparian states, water use is closely tracked by requiring users to apply for permits to withdraw water. In other states, where water has traditionally not been scarce, water use is not closely tracked. When there is a water shortage, water users share the shortage in proportion to their rights, or the amount they are permitted to withdraw, to the extent that it is possible to determine. Under the prior appropriation doctrine, water rights are not linked with land ownership. Instead, water rights are property rights that can be owned independent of land and are linked to priority and beneficial water use. A water right establishes a property right claim to a specific amount of water—called an allotment. Because water rights are not tied to land, water rights can be bought and sold without any ownership of land, although the rights to water may have specific geographic limitations. For example, a water right generally provides the ability to use water in a specific river basin taken from a specific area of the river. Water rights are also prioritized—water rights established first generally have seniority for the use of water over water rights established later—commonly described as “first in time, first in right.” As a result, once established, water rights retain their priority for as long as they remain valid. For example, a water right to 100 acre feet of Colorado River water established in 1885 would retain that 1885 priority and allotment, even if the right was sold by the original party who established it. Water rights also must be exercised in order to remain valid, meaning rights holders must put the water to beneficial use or their right can be deemed abandoned and terminated— commonly referred to as “use it or lose it.” When there is a water shortage in prior appropriation states, shortages fall on those who last obtained a legal right to use the water. As a result, a shortage can result in junior water rights holders losing all access to water, while senior rights holders have access to their entire allotment. For some states, the legal framework for groundwater is similar to that of surface water as they use variants of either the riparian or prior appropriation doctrine to allocate water rights. However, in other states, the allocation of groundwater rights follows other legal doctrines, including the rule of capture doctrine and the doctrine of reasonable use. Under the rule of capture doctrine, landowners have the right to all the water they can capture under their land for any use, regardless of the effect on other water users. The doctrine of reasonable use similarly affords landowners the right to water underneath their land, provided the use is restricted to an amount necessary for reasonable use. In some cases, permits may be required prior to use and additional regulation may occur if a groundwater source is interconnected with surface water. A number of state agencies may be involved in considering or approving applications to build power plants or to use water in power plants. In some states, a centralized agency considers applications to build new power plants. In other states, applications may be filed with multiple state agencies. State water regulators issue water permits for power plants and other sectors to regulate water use and ensure compliance with relevant state laws and regulations. Public Utility Commissions, or the equivalent, may also have a role in authorizing the development of a power plant. In many states where retail electricity rates are regulated, these commissions are primarily responsible for approving the rates (or prices) electric utilities charge their customers and ensuring they are reasonable. As part of approving rates, these commissions approve utility investments into such things as new power plants and, as a result, may consider whether specific power plant design and cooling technologies are reasonable.