Water is by far the largest component of fracking fluids. According to driller
Chesapeake Energy, an initial drilling operation itself may consume from 6,000 to 600,000 US gallons of fracking fluids, but over its lifetime an average well may require up to an additional 5 million gallons of water for full operation and possible restimulation frac jobs.
[1]
A 2009 report on modern shale gas by the Groundwater Protection Council,
"Modern Shale Gas Development in the United States: A Primer," stated that “[t]he amount of water needed to drill and fracture a horizontal shale gas well generally ranges from about 2 million to 4 million gallons, depending on the basin and formation characteristics.” A 2010 Harvard
study found that, on average, water consumption for natural gas produced through fracking ranges from 0.6 to 1.8 gallons of water per MMBtu (Mielke, Anadon and Narayanamurti 2010).
The extraction of so much water for fracking has raised concerns about the ecological impacts to aquatic resources, as well as dewatering of drinking water aquifers. It has also been estimated that the transportation of a million gallons of water (fresh or waste water) requires hundreds of truck trips, increasing the greenhouse gas footprint of oil and gas and contrbuting to air pollution.
[2] http://www.sourcewatch.org/index.php/Fracking_and_water_consumption