In the United States, 410 billion gallons of water are withdrawn for use each day. Almost half (49%) of this water is used by the power sector. On the other side, more than 12%of the nation's energy use is used to meet the country’s water and steam demand.
In other words - a lot of water is used for energy and significant energy is used for water.
This concept is at the core of a new bill in the U.S. Senate, which focuses on the connections between energy and water systems in the United States. The Nexus of Energy and Water for Sustainability (NEWS) Act of 2014 (S. 1971) defines the term energy-water nexus as the link between energy efficiency and the quantity of water needed to produce fuels and energy and the quantity of energy needed to transport, reclaim, and treat water.
In a statement last week on the bill, Senator Murkowski stated that "a coordinated public-private approach to energy-water nexus issues would promote economic growth and lead to the discovery of breakthrough technologies in energy and water resiliency." Specifically, the bill (as introduced by Senator Murkowski and Senator Wyden) would "establish an interagency coordination committee or subcommittee with the leadership of the Department of Energy and the Department of the Interior, focused on the nexus between energy and water production, use, and efficiency, and for other purposes."
This relationship between our water and energy systems was highlighted in a 2012 paper by Dr. Kelly T. Sanders (now a Professor at USC) and Dr. Michael E. Webber (a Professor at UT Austin) in Environmental Research Letters . In this paper, Sanders and Webber discuss the factors that influence the energy intensity of a volume of water. That is, the amount of energy that it takes to supply a quantity of water for different purposes. According to their research, this value is the function of many factors, including the:
1. initial quality of the water at its source
2. intended end-use and corresponding required sanitation level (for example, drinking water versus potable water requirements)
3. proximity of the water source to a water treatment facility and end-use location
4. energy-intensity of water treatment technologies (which are themselves a function of the size, concentration and type of contaminant that has to be removed)
As a result, the energy intensity of water varies widely across locations and seasons.
Sanders and Webber highlight the fact that, while public water supply withdrawals are much smaller than those for power plant cooling (7.4% and 49%, respectively), the former requires much more energy per unit volume. This fact stems from the US Environmental Protection Agency's (EPA) Safe Drinking Water Act (SDWA), which sets water quality standards for U.S. drinking water. In short – the water we drink is much cleaner than the water used to cool thermoelectric power plants.
Source: Sanders and Webber, 2012
Furthermore, the water that we use in our homes is generally pumped over longer distances than in other sectors. A power plant or farm will frequently pull its water from a nearby lake, river or well. But, our homes are spread out across wide areas, some of which are not close to the water treatment centers that supply the nation’s drinking water.
Sanders and Webber illustrated this use of energy for water in the following graphic:
According to Dr. Ory Zik the CEO of Energy Points, the Senate bill proposal would help to make the environmental impact of water use more transparent. It would also make the energy-water nexus more transparent moving forward. According to Zik, “The truth is that given enough energy, it is possible to provide water to any place in the world—that’s why water is really an energy issue. By measuring source energy (the energy invested in resources such as water and electricity) you’re able to directly compare resources in terms of energy and environmental impact.”
He went on to highlight an implication of the dependence of our energy systems on having large supplies of water, stating that “[it] may be that electricity conservation would be as impactful as water conservation, if not more, because of the vast amounts of water it takes to produce that electricity. Only source-to-site energy analysis can bring that to light.”
To learn more about Sanders and Webber’s research, a video summary of their 2012 paper can be found below:
To hear Senator Murkowski speak about the 2014 S.1971 proposal, see a speech that she gave earlier this year, which is largely based on the work of Sanders and Webber below:
Photo Credit: Photo of a water droplet by Michael Melgar.