Evaluating the Energy Intensity of the US Public Water System

Previous analyses have concluded that the United State’s water sector uses over 3% of national electricity consumption for the production, conveyance, and treatment of water and wastewater and as much as 10% when considering the energy required for on-site heating, cooling, pumping, and softening of water for end-use. The energy intensity of water is influenced by factors such as source water quality, its proximity to a water treatment facility and end-use, its intended end-use and sanitation level, as well as its conveyance to and treatment at a wastewater treatment facility. Since these requirements differ by geographic location, climate, season, and local water quality standards, the energy consumption of regional water systems vary significantly. While national studies have aggregated averages for the energy use and energy intensity of various stages of the of the US water system, these estimates do not capture the wide disparity between regional water systems. For instance, 19 percent of California’s total electricity generation is used to withdraw, collect, convey, treat, distribute, and prepare water for end-use, nearly doubling the national average. Much of this electricity is used to move water over high elevations and across long distances from water-rich to water-stressed regions of the state. Potable water received by users in Southern California has typically been pumped as far as 450 miles, and lifted nearly 2000ft over the system’s highest point in the Tehachapi Mountains. Consequently, the energy intensity of San Diego County’s water is approximately 11,000 kWh per million gallons for pumping treatment and distribution, as compared to the US average which is estimated to be in the vicinity of 1,500–2,000 kWh per million gallons. With added pressures on the state’s long-haul transfer systems from population growth and growing interest in energy-intensive desalination, this margin will likely increase. This manuscript consists of a first-order analysis to quantify the energy embedded in the US public water supply, which is the primary water source to residential, commercial, and municipal users. Our analysis finds that energy use associated with the public water supply is 4.7% of the nation’s annual primary energy and 6.1% of national electricity consumption, respectively. Public water and wastewater pumping, treatment, and distribution, as well as commercial and residential water-heating were considered in this preliminary work. End-use energy requirements associated with water for municipal, industrial, and self-supplied sectors (i.e. agriculture, thermoelectric, mining, etc.) were not included in this analysis.