U.N. World Water Day and the Energy-Water Nexus

March 25, 2014 by Jeff Shepard

In response to the UN World Water Day last Friday, the United Nations, Congressional Research Service and Pure Energies, Inc. all issued reports related to the "Energy-Water Nexus." Water and energy are resources that are reciprocally and mutually linked, because meeting energy needs requires water, often in large quantities, for mining, fuel production, hydropower, and power plant cooling, and energy is needed for pumping, treatment, and distribution of water and for collection, treatment, and discharge of wastewater. This interrelationship is often referred to as the energy-water nexus, or the water-energy nexus. Pure Energies issued an infographic that illustrates the link between water and energy, which shows that coal-fired plants consume the most water needing up to 1,000 gallons per MWhr, nuclear generation is second consuming up to 800 gallons per MWhr, natural gas generation demands up to 300 gallons per MWhr, while solar power needs no water.

There is growing recognition that “saving water saves energy.” Energy efficiency initiatives offer opportunities for delivering significant water savings, and likewise, water efficiency initiatives offer opportunities for delivering significant energy savings. In addition, saving water also reduces carbon emissions by saving energy otherwise generated to move and treat water.

This report provides background on energy for facilities that treat and deliver water to end users and also dispose of and discharge wastewater. Energy use for water is a function of many variables, including water source (surface water pumping typically requires less energy than groundwater pumping), treatment (high ambient quality raw water requires less treatment than brackish or seawater), intended end-use, distribution (water pumped long distances requires more energy), amount of water loss in the system through leakage and evaporation, and level of wastewater treatment (stringency of water quality regulations to meet discharge standards).

Likewise, the intensity of energy use of water, which is the relative amount of energy needed for a task such as pumping water, varies depending on characteristics such as topography (affecting groundwater recharge), climate, seasonal temperature, and rainfall. Most of the energy used for water-related purposes is in the form of electricity. Estimates of water-related energy use range from 4% to perhaps 13% of the nation’s electricity generation, but regional differences can be significant. In California, for example, as much as 19% of the state’s electricity consumption is for pumping, treating, collecting and discharging water and wastewater.

Energy consumption by public drinking water and wastewater utilities, which are primarily owned and operated by local governments, can represent 30-40% of a municipality’s energy bill. At drinking water plants, the largest energy use (about 80%) is to operate motors for pumping. At wastewater treatment plants; aeration, pumping, and solids processing account for most of the electricity that is used. Energy is the second highest budget item for these utilities, after labor costs, so energy conservation and efficiency are issues of increasing importance to many of them.

Opportunities for efficiency exist in several categories, such as upgrading to more efficient equipment, improving energy management, and generating energy on-site to offset purchased electricity. However, barriers to improved energy efficiency by water and wastewater utilities exist, including capital costs and reluctance by utility officials to change practices or implement new technologies.