How much water does a nuclear power plant consume?
First, a definition and some generalisations. Consumption is the net water loss from evaporation and equals the amount of water withdrawn from the source minus the amount returned to the source. With cooling towers, the amount of water withdrawn from the source is similar to consumption. With once through cooling, withdrawal is vastly greater than consumption. But overall consumption is greater with cooling towers than with once through cooling. Generally, cooling towers reduce the impacts on aquatic life but increase water consumption. For coastal sites, the loss (consumption) of water is rarely if ever a problem but the impacts on marine life (and other environmental impacts) can be significant.
Woods  gives figures of 1,514 to 2,725 litres of water consumption per megawatt-hour (MWh) for nuclear power reactors and the Nuclear Energy Institute gives identical figures. For a 1 GW reactor, that equates to daily water consumption of 36.3 to 65.4 million litres. The lower figure is for once-through cooling, the higher figure is for systems using cooling towers (a.k.a. closed-loop, recirculating).
A 2009 World Economic Forum (WEF) paper gives a near-identical figure for closed-loop cooling (2,700 l/MWh) − plus 170−570 l/MWh for uranium mining and fuel production, giving a total of 2,870 to 3,270 l/MWh (68.9 to 78.5 million litres daily) .
For coal, the WEF paper gives figures of 1,220 to 2,270 l/MWh (including mining).
For gas, the WEF paper gives figures of 700 to 1,200 l/MWh, and the Nuclear Energy Institute gives figures of zero (dry cooling) to 380 l/MWh (once through cooling) to 1,400 l/MWh (cooling towers).
The Nuclear Energy Institute claims that hydro plants consume 17,000 l/MWh, largely due to evaporation from reservoirs. The Nuclear Energy Institute further states that "renewable energy sources such as geothermal and solar thermal consume two to four times more water than nuclear power plants", without providing any details or references, and without noting that some renewable energy sources (such as wind and solar PV) use negligible water.
Some nuclear advocates promote the potential role of nuclear power in addressing some water problems, e.g. low-carbon desalination. But such proposals raise familiar problems − for example Syria's pursuit of a nuclear-powered desalination plant may have masked weapons ambitions and is believed to have been abandoned because of US pressure. Nuclear advocates are on stronger ground when they note that there is no need for nuclear plants to be located adjacent to their fuel source (typically 180 tonnes of low enriched uranium fuel annually for a 1 GW reactor); thus for example inland coal-fired power plants adjacent to coal mines can be replaced by coastal nuclear plants.
The Union of Concerned Scientists gives the following figures for water withdrawal (as opposed to consumption):
- with closed-loop recirculating cooling, water withdrawal ranges from 3,000−9,800 l/MWh (72−235 million litres daily for a 1GW reactor);
- with once through cooling, withdrawal is far greater at 95,000−227,000 l/MWh (2.3−5.4 billion litres daily for a 1 GW reactor; 0.84−1.97 trillion litres annually).
The Nuclear Information and Resource Service notes that a typical once-through cooling system draws into each reactor unit more than one billion gallons (3.8 billion litres) of water daily, 500,000 gallons (1.9 million litres) per minute.
 Guy Woods, Australian Commonwealth Department of Parliamentary Services, 2006, 'Water requirements of nuclear power stations', http://efmr.org/files/07rn12.pdf
 World Economic Forum in partnership with Cambridge Energy Research Associates, 2009, 'Energy Vision Update 2009, Thirsty Energy: Water and Energy in the 21st Century', http://www3.weforum.org/docs/WEF_WaterAndEnergy21stCentury_Report.pdf
 Nuclear Energy Institute, November 2012, Water Use and Nuclear Power Plants, www.nei.org/Master-Document-Folder/Backgrounders/Fact-Sheets/Water-Use-a...
 Union of Concerned Scientists, July 2013, 'Water-Smart Power: Strengthening the U.S. Electricity System in a Warming World', www.ucsusa.org or http://tinyurl.com/ucs-water
 Nuclear Information and Resource Service, 'Licensed to Kill', www.nirs.org/reactorwatch/licensedtokill