The Water-Energy Nexus

Major droughts have driven awareness of water scarcity and it is important to understand the demands that energy-intensive activities place on water resources.

Major droughts from California to South Africa have driven awareness of water scarcity. Many organizations are measuring, managing and reporting on their direct water consumption to address drought risks. However, there is not yet an accepted and easy-to-implement methodology for quantifying unseen, upstream consumption of water. With increasing demands for water alongside dwindling supplies—due to climate change, drought and the competing demands from industrial, agricultural and municipal water users—it is important to understand the demands that energy-intensive activities place on water resources. The water-energy nexus is a useful lens for analyzing policy or resource management in a specific geography.

While there are many definitions of the water-energy nexus, one version highlights the relationship between the upstream water consumption (e.g., water pumped into a well for oil extraction) and water used during electricity generation (e.g., water evaporated from cooling towers). Every form of electricity generation—even renewables like solar and wind—requires water.  As a result, downstream water availability and quality is often impacted by upstream energy production.1 These impacts are not only caused by direct water consumption during resource extraction and electricity generation, but also by indirect means such as contamination of water following extraction (e.g., from coal mining tailings). 

To date, much focus has been on the greenhouse gas (GHG) emissions from electricity production, while less attention has been paid to the amount of water required to produce electricity, despite electricity generation withdrawing more water in the United States than any other use category. The direct water impacts from electricity production, combined with the indirect impacts of climate change in altering water availability, makes electricity a powerful water topic.

LCA Reveals Complexities and Tradeoffs

Just as GHG emissions factors vary from one grid to another, so does water impact intensity. Understanding how water impacts vary can be useful to organizations that are large consumers of electricity and want to account for and manage water consumption in addition to GHG emissions. For example, some data centers use a significant amount of water for on-site cooling with a water-cooled HVAC system. This direct water consumption could be reduced by switching to cooling technologies that do not require direct water consumption (e.g., air-cooled HVAC systems), but instead, require more electricity. Often, using more electricity results in higher GHG emissions and the water required to generate electricity for cooling the data center could have a large water footprint. Life cycle assessment (LCA) is a powerful tool for examining these tradeoffs.

In LCA, “blue water” is freshwater from surface and groundwater sources and “water consumption” is the portion of water use that is not returned to the original water source after being withdrawn and is no longer available for reuse (e.g., water lost via evaporation or water incorporated into a product or plant.) Therefore, blue water consumption (BWC) is a measure of the net freshwater made otherwise unavailable to a region and is an important metric to consider when examining the potential to exacerbate water scarcity in a particular location.

The map below illustrates both global warming potential (GWP) and BWC from the U.S. eGRID electricity generating regions. The darker the blue color of the region, the more water is consumed in generating the electricity for that region. The larger the factory icon in that region, the higher its GHG emissions. From this map, it becomes clear that there are regions where electricity has high BWC, but low GHG emissions (e.g., Pacific Northwest (NWPP), and vice-versa (e.g., Texas (ERCT).

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Figure 1. Water and GHG Emissions from Electricity Generation by eGRID Region

The NWPP eGRID region has notably high embedded water, but low GHG emissions. This region’s grid mix is primarily hydropower (52%) and coal (25%). For comparison, the ERCT eGRID region has low embedded water, but high GHG emissions. This region’s grid mix is primarily natural gas (49%) and coal (31%)2. This map illustrates that there are often tradeoffs between GHG emissions and BWG.

An example of this is hydropower, which has the highest embedded water and the lowest GHG emissions of all energy generation types. Within hydropower, there are three types of generation — run-of-river, storage and pump storage. Storage and pump storage hydropower have high embedded water because water is lost to the watershed (consumed) through evaporation from the open surface of water in a reservoir. Studies have demonstrated that an average of 1.5 m3 of water can be lost to evaporation per gigajoules (GJ) of electricity produced, but this water loss can range from 0.01 to 53 m3 of water per GJ of electricity3. Even though coal, natural gas and nuclear rely on steam to generate electricity, the quantity of water lost to the atmosphere (consumed) is lower than that of hydropower per GJ. The water consumption of renewables such as photovoltaics and wind are comparatively low since the generation of power by these technologies does not require evaporating water.

Conclusions

The water-energy nexus illustrates that water scarcity and GHG emissions are inextricably tied as environmental impacts that will shape the future of the planet; thus, they are equally important considerations for organizations aiming to set targets to reduce their environmental footprint. The tradeoffs between GHG emissions and BWC become apparent through the example of electricity generation, but this is not the only example of these types of tradeoffs. The information that LCA provides can help organizations discover these tradeoffs and evaluate options for addressing them to arrive at beneficial solutions that optimize environmental outcomes and achieve goals and targets.

WSP is currently working with the World Resources Institute (WRI) to develop an accounting methodology for Scope 2 water impacts or the water impacts during the production of electricity. Learn more about this methodology through our Insights article, Developing Improved Approaches to Water Stewardship.


1 Cooley, H., Fulton, J., & Gleick, P. (2011, November). Water for Energy: Future Water Needs for Electricity in the Intermountain West (publication). Retrieved http://www2.pacinst.org/wp-content/uploads/2013/02/water_for_energy1.pdf

2 US EPA, US eGRID files 1996-2014 https://www.epa.gov/energy/emissions-generation-resource-integrated-database-egrid

3 Mekonnen and Hoekstra, “The blue water footprint of electricity from hydropower,” Hydrology and Earth Systems Science. 2012. http://www.hydrol-earth-syst-sci.net/16/179/2012/hess-16-179-2012.pdf

 


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