Approximately 65% of the California’s water supply is in Northern California while 65% of water demand is in Southern California. California’s water conveyance system requires an enormous amount of energy to transport water through hundreds of miles of canals and pipelines and dozens of pump stations from the north to the south. Water treatment, distribution and wastewater treatment also require significant energy. A set of studies recently completed for the California Public Utilities Commission estimated that about 7.7% of the state’s total electricity requirements are used every year by the water infrastructure.
A simple diagram of the water use cycle is used as a framework for identifying and qualifying opportunities to optimize the net resource, economic and environmental benefits of the state’s water and energy resources and infrastructure. Opportunities to optimize water and energy in combination exist in all segments of the water use cycle.
California's Water Cycle
To help quantify the opportunities for energy savings in the water sector, the CEC introduced the concept of energy intensity as a means of expressing the relative magnitude of water-energy relationships.
“Energy intensity is defined as the amount of energy consumed per unit of water to perform water management-related actions such as desalting, pumping, pressurizing, groundwater extraction, conveyance, and treatment - for example, the number of kilowatt-hours consumed per million gallons (kWh/MG) of water. This concept is applied to water supplies, to components of the water use cycle, and to the total energy intensity of a unit of water throughout the entire water use cycle.1”
The energy intensity of future water supplies (marginal supplies) is expected to increase dramatically due to increased pumping requirements, higher treatment energy use by brackish and seawater desalination, and more stringent treatment requirements for discharge of wastewater. For example, the average energy intensity of untreated water supplied to Southern California is approximately 3,500 kWh/MG; however, the energy intensity of marginal supplies ranges from 3,500 to 12,200 kWh/MG.
Key strategies to keep energy costs from sharply increasing as a result of increased reliance on marginal water supplies include: conserving water, investing in energy efficient water infrastructure, new technologies to reduce energy use by marginal supplies, and expanding the use of recycled water (a less energy intensive supply). Additional actions are detailed in the next section: Measures.
1California Energy Commission. California’s Water-Energy Relationship. CEC-700-2005-011-SF. November 2005.