When I hear the term “water-energy nexus,” I imagine something complex and fantastical, when in actuality it is an intimately familiar and essential component to most of our lives. Water and energy are closely connected in a multitude of ways, from cooling the power plants that produce our energy to pumping water to crops and our kitchen taps. The water-energy nexus is a field of study devoted to understanding and innovating around the interconnected nature of energy and water in the modern world.

In a recent study at Itron, we take a close look at energy reductions associated with the provision of water to end users in California when statewide water use is reduced due to severe drought conditions. Producing and transporting potable water to end users in California alone accounts for 7 percent of the state’s total annual electricity consumption.  Even more surprising, this large figure doesn’t even include waste water treatment or energy inputs by end users such as water heating, which on average accounts for 20 percent of the average household’s energy usage. It makes sense then that consuming less water results in less water pumped, less water heated, and less energy consumed. So why then do most of us view water and energy as unrelated? It’s not a unique phenomenon. When we purchase food at the grocery store, clothes online, or water from our taps, we tend to think we are paying for the resource or commodity itself. We don’t typically consider that a portion of our payment is for the embedded energy required for extraction, processing, and delivery of materials associated with those goods and services, including water. We all learn that water flows freely downhill with gravity, but few of us appreciate that our water delivery system is a reversal of this process requiring significant energy inputs.

In 2015, Governor Jerry Brown mandated a 25 percent reduction in urban water use relative to 2013 levels in response to falling water table levels and dwindling snowpack after years of sustained drought and increased reliance by agriculture and urban areas on groundwater pumping. The 2015 sharp reduction in urban water use following the mandate provided a natural experiment for Itron’s study that focuses on estimating energy savings associated with urban water conservation.

The study relies on water agencies’ monthly electric bills associated with groundwater pumping, water treatment, and distribution between the baseline year of 2013 and the mandate year of 2015 to empirically derive an energy savings estimate coincident with the state’s water conservation mandate. Itron evaluated electric billing data across 32 water agencies that are broadly representative of the state’s diversity in water system sources. The study also serves as a cross-check on the pre-existing water-energy calculator developed by the California Public Utilities Commission (CPUC) for use by the state’s investor-owned utilities. The existing water-energy calculator relies on a set of static values at the granularity of the state’s 10 hydrologic regions as determined by the California State Water Board.

Results of the study show that the relationship between water and energy in California is highly variable and unique to each water agency. Across the 32 water agencies in the study, Itron finds the energy embedded in urban water production and distribution ranges from approximately 300 to 500 kWh per acre-foot, with a weighted average of 397 kWh per acre-foot in 2015. These values corroborate prior findings that the energy reduction potential from water conservation is substantial, however, preliminary findings do show that the CPUC water-energy calculator overestimates energy savings by 20-30 percent. In addition, the static approach of the CPUC water-energy calculator is found to mask significant year to year variability in the energy intensity of water production related to drought intensification and changes in water management policy, indicating that there is still a lot of research necessary if it is to be a viable planning tool.

When we learn something as foundational as that water flows downhill, we often take for granted its significance, when in fact water’s downhill passage has the power to shape mountains and carve canyons. The core concept of the water-energy nexus is simple but similarly very powerful. Ultimately, energy reductions from water conservation represent an underestimated energy saving resource that can be leveraged by any state to assist in meeting GHG emission and energy saving goals. We have the preliminary data now to re-envision water conservation as a combined energy saving opportunity. The integration of water-energy savings into portfolio level planning requires significant research to catch up to the rigor of energy programs savings analysis and will require the corroboration of all groups for the aggregation of applicable data. The water-energy nexus is ultimately part of a larger movement towards fully integrated systems that can be comprehensively managed and optimized by policymakers and implementers.