There is a Water-Energy Nexus. But It’s Not What You Think.
NRDC, August 12, 2016
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 my colleague 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.