Two Case Studies Describe Significance of Energy Embedded in Water

The energy and greenhouse gas reductions that can be acheived through water conservation and efficiency are on par with other energy saving measures currently being pursued by municipalities such as the City of Guelph.
Author: Bevan Griffiths-Sattenspiel

A new paper written by researchers from the United States and Canada features two case studies that clearly describe why the energy embedded in water needs to be incorporated into water supply and wastewater management decisions.

The paper, titled Incorporating Energy Impacts into Water Supply and Wastewater Management was written by Sharon deMonsabert and Ali Bakhshi from George Mason University, Carol Maas with the POLIS Project on Ecological Governance and Barry Liner from Applied Engineering Management Corporation. You might remember Carol Maas from some previous posts I’ve written, including The Soft Path Approach and a post on The POLIS Water Sustainability Project.

The paper was peer-reviewed and included as part of the American Council for an Energy Efficient Economy’s 2009 Summer Study on Energy Efficiency in Industry. (Note: the paper can be purchased from ACEEE here)

Case 1: Embodied Energy for Water and Wastewater

The first case study “compares the embodied energy of water use to appliances in American homes that are typically considered by environmental rating and energy efficiency programs. The study focused on “the municipal embodied energy required for the production, delivery, and disposal of water in an urban water system,” not the energy embedded at end-uses.

The study began by comparing two different scenarios for water users in Northern Virginia: a residence located at 50 ft. above sea level and a residence located at 200 ft. above sea level. The following noteworthy conclusions were determined through this case study:

  • In both residences, the estimated carbon footprint of the embodied energy for water use was greater than 630 lbs. per year.
  • A change in elevation, of 150 ft. in this case, increases CO2 emissions by 35%.
  • Even with a small difference in elevation between the water treatment plant and the end-user (in this case the treatment plant was located at sea level), the embodied energy for water and wastewater is greater than most common residential appliances.
  • Of the appliances studied, only inefficient lighting (100 watt light bulbs) exceeds the embodied energy CO2 emissions for the water and wastewater industries.

As this study clearly demonstrates, a number of appliances targeted for regulations and/or energy conservation programs such as EnergyStar, actually result in fewer annual greenhouse gas emissions than water. Which begs the question: why not include water efficiency in energy conservation programs?

It is important to keep in mind that this study looked only at the municipal energy requirements – or “upstream” and “downstream” embodied energy – for water, not the additional energy required to heat, cool, purify or pressurize water at end-uses. As we found in The Carbon Footprint of Water, water heating alone accounts for nearly 75% of the energy and carbon embedded in the water we use. Therefore, the energy/carbon savings are even greater when end-uses are included.

In the tables below you can find the tables comparing the energy and carbon emissions required to supply and treat water and wastewater with the energy and carbon emissions associated with typical household appliances.

Tables comparing energy embedded in water to energy used by typical household appliances, download larger image below
For full methodological details, see deMonsabert, S, Bakhshi, A, Headley, A (2008)., Embodied Energy in Municipal Water and Wastewater, Sustainability 2008-. Green Practices for the Water Environment.

Case 2: Water and Energy Conservation

The second case study highlighted in the paper, “explores the energy savings achievable through reduced water use, stemming from municipal water conservation programs.” The study looked at the City of Guelph, a medium-sized city with a population of 115,000 supplied by groundwater. As the authors describe (emphasis added):

  • Guelph is a progressive community with both well established water conservation planning and a community energy plan. The City’s Water Conservation and Efficiency Strategy is targeting a total water use reduction of 20 per cent from the projected business as usual scenario in 2025, an equivalent water savings of 10,600 m3/d. This target offers significant water and energy savings benefits for Guelph.*

In addition to water savings, the following benefits would also be realized if Guelph meets their water conservation target:

  • Municipal electricity savings stemming from water conservation of more than 2400 MWh/yr, enough electricity to provide half of the pumping energy used for source extraction from the City’s wells in 2006.

  • At today’s electricity prices ($0.06/kWh), in 2025 the City could save more than $2700/week in water and wastewater electricity expenditures alone.

  • The electrical energy savings achieved through water conservation were found to be on par with other energy efficiency and greenhouse gas mitigation measures currently being pursued in Guelph, such as powering the Woods Pumping station with green energy, which could offset the GHG emissions from generating an estimated 2.8 million kWh/yr.

As these case studies show, there are a number of opportunities for water and wastewater utilities to save large amounts of energy. In a later post I will the three ways to incorporate energy impacts into water supply and wastewater management described in this Incorporating Energy Impacts into Water Supply and Wastewater Management. Here’s a complete citation of the paper:

deMonsabert, S., Maas, C., Bakhshi, A., and Liner, B. "Incorporating Energy Impacts into Water Supply and Wastewater Management." (2009) American Council for an Energy-Efficient Economy (ACEEE) Summer Study in Industry, July 28-31, Niagara Falls, New York

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