I. Introduction

A number of studies published in the last few years anticipate a water crisis in many regions of the United States driven primarily by electricity generation water demand. (Avery, 2011, Sovocool, 2009 and Roy, 2012). A careful review of these studies and other studies addressing the so-called energy-water nexus, however, indicate that a crisis is not at hand in most if not all of these regions even accounting for potential droughts attributed to climate change. These "crisis" studies reflect similar metrics or assumptions that explain their somewhat alarmist conclusions. First, they all focus on water withdrawals rather than water consumption as the basis for measuring water demand. Second, they all assume no water demand or supply side response to rising water prices that are likely to accompany growing water scarcity. Third, they do not account for changing technologies prompted by expected relative energy prices and public policies that affect both water supply and demand. As discussed below, focusing on water consumption rather than withdrawal and accounting for both demand and supply responses to rising water prices related to scarcity, greatly diminishes or eliminates the likelihood of water shortages and electricity blackouts.

II. The Electricity-Water Nexus

A great deal of attention has been paid to the relationship between electricity generation and water supply especially in the face of recent drought conditions in various parts of the country and projections of reduced rainfall attributed to climate change. In a few instances power plant operations have been constrained by water shortages and proposed power plants have been delayed or rejected over water concerns. Electricity generation is often identified as a very large water consumer suggesting that future water shortages will result in substantial constraints on electricity production. At the same time, water supplies require electricity for treatment, pumping, and conveyance. Thus, the specter of simultaneous water and electricity shortages arises.

This fear, however, is misplaced. The nexus between water and electricity is relatively modest. Electricity generation does not demand a particularly large share of water supply. As shown in Figure 1, electricity accounts for only 4% of U.S. water consumption. Only when water withdrawal is considered, does electricity generation appear to represent a large share of water use. As shown in Figure 2, electricity accounts for 49% of withdrawals. This is misleading because as much as 96% of water withdrawn by power plants is returned to the water supply.

Reliance on withdrawals to estimate water supply stresses is problematic. To the extent withdrawals are relevant, the crisis studies do not take into account how water networks operate within a given watershed to realistically determine whether a water shortage will occur. In brief, the order of withdrawals matters. To see this, one can consider two very simple watersheds with exactly the same water supply of 50,000 gallons from a single river, and three users with similar withdrawal and consumption characteristics in each watershed (here representing the agricultural, thermoelectric, and residential sectors), as illustrated in Figure 3. The only difference in the two watersheds is the order in which these users draw water from the river. Despite identical total withdrawals one watershed has sufficient water to meet demand, the other does not. In the first watershed, the agricultural user is located up river and withdraws 50,000 gallons and consumes 10,000 gallons, returning 40,000 gallons to the river. A power plant is located mid-river, withdrawing 40,000 gallons, consuming 10,000, and returning 30,000 gallons. Thus, downriver of the power plant, there are 30,000 gallons available, meeting the residential user's requirements so that no water user is constrained. In the second watershed, however, the power plant and residential user switch positions along the river. In this example, after the residential user's consumption mid-river, only 35,000 gallons remain for downstream use by the power plant, leaving it unable to meet its demand of 40,000 gallons. Though obviously oversimplified, this example reveals that stress on water supplies is partially dependent on the organization of users within a water network. Calculating total withdrawals alone is insufficient to accurately diagnose water supply stresses. Not surprisingly, state water planners consider water consumption rather than withdrawals when establishing water availability. This is not to say the for any given water system that withdrawals may pose constraints on access, but that any broad assessment of water shortages will be misleading if it relies on withdrawals as the key measure of water demand.

It is also important to consider the other side of the nexus – the demand for electricity by water suppliers. This demand is modest on a relative scale. Even in California, where long distance conveyance is much more extensive than most other states, water related electricity demand accounts for 19% of total electricity consumption.1 This figure, however, accounts for electricity for the entire water cycle, which includes pumping, treatment, conveyance, distribution, and waste water treatment, as well as residential, agricultural and industrial end use. Electricity for supply, treatment, and conveyance accounts for only about 4% of state electricity demand.

Finally, students of the nexus have also raised concerns regarding water use in fossil fuel extraction. Water use related to coal mining and water used in natural gas fracturing have been cited as important sources of water demand. The evidence, however, does not support this. Overall demand for water for energy resource extraction is very modest, under 10% of U.S. water consumption. Mielke et al. (2010) report that coal mining water consumption averages 2.6 gallons/mmbtu, conventional natural gas well consumption is near zero, and shale gas consumption averages 1.3/gallons/mmbtu. Although Freyman (2014) conclude that over half of the oil and gas wells associated with fracking are in water stressed locations, there is reason to consider this an overstatement. First, as noted by Kimball (2013) the study relies on water withdrawals not consumption. Second, the study relies on county level comparisons even though water suppliers rarely conform to county borders. For example, a recent study of fracturing demand in Texas (Nicot, 2012), a major source of shale gas production, found that water consumption represented less than 1% of water demand at the state level. The study noted that the fraction of water demand in smaller regions was higher, but also noted that greater reliance on brackish water and less water intensive technologies would allow further shale gas production even in these regions. Thus, overall water demand for resource extraction will fall as the generation mix shifts from coal to natural gas and renewables.

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Footnotes

1 California's water supplies are located primarily in the northern part of the state, while the largest share of water demand is accounted for in the south. (California Energy Commission 2005).Extensive pumping is required to move this water from north to south.  

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