Embedded Energy and Water-Energy Nexus

It is easy to forget that energy is needed to collect and treat the wastewater that comes from our sinks, showers, toilets, clothes washers, and other sources. This energy use is referred to as  embedded energy.

Earlier this summer, researchers at UC-Davis confirmed what a lot of us already know—that saving water saves energy.

The analysis from the UC-Davis Center for Water-Energy Efficiency found that California’s mandatory 25 percent reduction in urban water use, which was adopted in May 2015 due to the ongoing severe drought, resulted in significant energy and greenhouse gas savings.

From June 2015 to February 2016, the electricity saved by reducing urban water use is estimated to have been nearly 922 gigawatt-hours.

Because electricity production oftentimes relies on fossil fuels like coal and natural gas, this energy savings also significantly reduced greenhouse gas emissions—similar in scale to taking almost 50,000 cars off the road!

Saving water saves energy because of the large amount of energy needed to extract, transport, treat, and distribute water to our homes and businesses.

Still more energy is needed to collect and treat the wastewater that then comes from our sinks, showers, toilets, clothes washers, and other sources. This energy use is referred to as  embedded energy .

In California, the embedded energy in water can be quite large, especially for regions like Southern California, which rely heavily on imported water supplies from the Sacramento-San Joaquin Bay Delta and the Colorado River.

To divert water from one river basin to another, major facilities pump water over long distances and steep terrain. In fact, roughly half of the energy embedded in water in California comes from the state's major long-distance conveyance systems—the State Water Project (SWP) and the Colorado River Aqueduct (CRA).

The former conveys water that falls as rain or snow in the northern part of the state, and the latter conveys water from the Colorado River.     

As  Ed Osann explained last fall, NRDC has been involved for several years in a proceeding at the California Public Utilities Commission that focused on estimating how much embedded energy can be reasonably saved by investing in end-use water-savings measures.

While energy and water utilities are now moving forward with use of the calculator tools approved by the Commission, there is a distinct possibility that the embedded energy savings attributed to end-use water efficiency measures could be significantly exaggerated unless the limitations of the calculator tools are more clearly recognized.

For example, while the calculator accurately assesses the benefits of water efficiency in reducing the energy used to treat and distribute water to the customer, it likely overestimates the benefits of water efficiency in reducing the energy used to move water long distances.

The energy used by most local utilities that treat and distribute water to retail customers (i.e., energy used by your local drinking water treatment plant) can certainly be reduced through water conservation and efficiency.

But while the movement of treated drinking water is generally in sync with the demands of water users, the  conveyance  (i.e., pumping over long distances) of untreated water from its natural source to a carry-over storage facility is primarily driven by source water availability and may not be influenced by reductions in end-use water demand for many years or even decades.

The SWP and CRA systems purposefully store untreated water to buffer against large fluctuations in water supply due to year-to-year changes in the amount of water available from rain or snowpack. Because of the significant embedded energy related to conveying water over long distances to these carry-over storage facilities, there is the potential for the calculator tools to overstate the energy savings attributable to end-use water conservation measures.

This is particularly true if other state agencies (e.g., Air Resources Board, State Water Resources Control Board, Department of Water Resources) utilize the calculator tools without imposing the same restrictions that the Commission has put in place, such as only allowing embedded energy savings from investor-owned utilities (IOUs) to be claimed.

The energy used by SWP and CRA operations primarily comes from public power agencies so by only considering IOU energy, the embedded energy due to water conveyance is rightfully excluded as a potential source of energy savings for end-use water conservation efforts. Notably, UC-Davis researchers follow the Commission’s approach by only considering embedded energy from IOUs in their analysis.   

To more fully illustrate the embedded energy and long-distance water conveyance conundrum, we analyzed the energy consumed by the SWP and the CRA since the beginning of the drought in 2010. It’s important to note that drought conditions in California have affected the water available to the SWP whereas water for the CRA comes from the Colorado River Basin, from which California has continued to withdraw its full allotment under the applicable interstate compacts.

Due to the severity of California’s drought, the California State Water Resources Control Board (SWRCB) imposed mandatory water conservation targets on urban water suppliers in May 2015.

If end-use water conservation had an immediate or relatively near-term impact on long-distance water conveyance, we would expect to see a fairly distinct inverse relationship between water conservation rates and SWP and CRA energy consumption. In other words, we would expect that as more water is conserved, SWP and CRA energy consumption would also decrease because less water is conveyed.

Read full article at: NRDC

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Taxonomy

• Wastewater Use
• Energy
• Water-Energy Nexus
• Energy
• Energy Conservation