The Water-Energy Nexus and Why it Matters

August 10, 2022

With the effects of climate change being felt all over the world, and California in the midst of another severe drought, we thought we would share more about our initiative to address the important connection between our warming planet and the water we all need to survive: The Water-Energy Nexus Registry.

What is the Water-Energy Nexus?

To put it simply, moving, treating, and using water requires energy, and providing energy to businesses and homes requires water. Every step of the water cycle uses energy. The Climate Registry’s (TCR) focus on the water-energy nexus centers on the energy required to extract, convey, and deliver water of appropriate quality for diverse human uses, and then again to treat waste waters prior to their return to the environment. The sources of energy used to power water activities are directly tied to the volume of greenhouse gases (GHG) we emit into the atmosphere.

Energy is required to pump water from underground aquifers, move water from one location to another, treat water to make it drinkable, and heat and cool water. It takes a significant amount of energy to get water to our taps or to move it away after it goes down our drains. During drought years, which are anticipated to become more common in the coming decades with climate change, the energy requirements for these processes can become even greater. This effect is already being felt in the state of California, where the California Air Resources Board (CARB) is directed by law to reduce GHG emissions to 40 percent below 1990 levels by 2030. In CARB’s 2017 Climate Change Scoping Plan, water is identified as a key emissions source, with local agencies playing an important role in delivering this resource. CARB’s goals within this Plan include support for increasing water sector energy efficiency and reducing GHG emissions through reduced water and energy use.

To support the Plan’s water sector GHG reduction goals, the California State Legislature passed Senate Bill 1425 in 2016, requiring CARB’s parent agency, the California Environmental Protection Agency (CalEPA), to oversee the development of a voluntary registry for GHG emissions resulting from the state’s water-energy-GHG nexus. Based on experience successfully operating a voluntary GHG emissions registry, TCR was selected by CalEPA to develop and manage the Water-Energy Nexus Registry with the aim of providing a meaningful and standardized resource to the water sector to promote climate action and emissions reductions aligned with the State’s climate change scoping plan.

TCR’s Water-Energy Nexus (WEN) Registry program gives stakeholders the tools to track the relationship between water use and GHG emissions, and provides comprehensive consulting, training, and data collection support. This technical assistance is extremely beneficial to the water sector to ensure decision-making for infrastructure and clean drinking water projects includes consideration of GHG and other climate impacts. Determining the energy intensity of water helps utilities, regulators, and consumers make water decisions aligned with the GHG emissions reduction goals and have a positive impact on climate change mitigation. The data can help water agencies develop, implement, and monitor Climate Action and Resilience Plans with GHG reduction targets that align with or even exceed the State’s goals. These plans can contain robust carbon strategies along with co-benefits such as cost savings and resilience. Additionally, such plans can be designed to minimize environmental impacts associated with system upgrades, capital improvement projects, and recycled water projects.

Leaders in the California water sector – such as the CA Department of Water Resources, Los Angeles Department of Water & Power, Metropolitan Water District of Southern California, and Sonoma Water – participate in the WEN Registry and are leading the charge to define how utilities can operate to reduce carbon emissions and make operational decisions to mitigate the worst effects of climate change. For downstream users of water who want to assess their own carbon inventory, understanding the energy component of the water used in their utility operations through identification of a performance metric (emission factor) is critical.

With the goal of providing standardized accounting guidance for the measurement, tracking, and mitigation of the greenhouse gas emissions associated with California’s water system, TCR continues to enable organizations to voluntarily support the state’s climate goals. Now more than ever, as we continue to see the acceleration of climate impacts, including worsening water scarcity and drought in the West, the WEN Registry is a critical tool in our arsenal to fight climate change.

For more information visit on TCR’s Water-Energy Nexus Registry,