General Assumptions

Variable Value Source & Notes
Electric Rate (U.S. Residential) $0.1151/kWh Source: 2011 U.S. Electric Rate: Energy Information Administration, Annual Energy Outlook 2011 (Early Release) edition, (Converted from 2009 to 2010 dollars)
Natural Gas Rate (U.S. Residential) $10.79/Mbtu Source: 2012 U.S. Gas Rate: Energy Information Administration, Annual Energy Outlook 2012 (Early Release) edition, (Converted from 2010 to 2011 dollars)
CO2 Emissions Rate 1.54 lbs. CO2/kWh Source: EPA’s Climate Change Action Plan (CCAP number for 2010)
Cost of a gallon of water $0.00837 Source: Based on data from American Water Works Association and Raftelis Financial Consultants, Inc, 2010 Water and Wastewater Rate Survey, 2011
Cubic feet required to heat one gallon 0.8768
Heated water from a tap or showerhead 73% Mayer, Peter W. and William B. DeOreo. The End Uses of Hot Water in Single Family Homes from Flow Trace Analysis. Aquacraft, Inc.
Cost of kWh of electricity $0.1178 http://www.eia.doe.gov/steo
Cost of cu ft of natural gas $0.01100 http://www.eia.doe.gov/steo
Btu per kilowatt-hour 3,412.14 http://www.onlineconversion.com/energy.htm
Weight of one gallon of water (pounds) 8.35 http://www.onlineconversion.com/waterweight.htm
% of households in the United States that heat water using electricity 41.09% Source:  American Housing Survey (AHS), 2009.  Note that 55.35% of U.S. homes use natural gas and a small portion of houses use alternate means of heating hot water (oil, solar, ground source, etc.).
Water heating process is about 90 percent efficient for electric hot water heaters 0.9 http://www.aceee.org/consumer/water-heating
kWh of electricity to heat one gallon of water, assuming incoming water is raised from 55° F to 120° F (D 65° F), and assuming 90% heating efficiency. 0.1766
Gallons saved per capita per day with WaterSense showerheads 2.4554
One cup of coffee is equivalent to…. 0.0625 gallons
One load of dishes is equivalent to…. 8.7 gallons
One shower is equivalent to…. 17.2 gallons
One load of laundry is equivalent to…. 40.9 gallons
One backyard swimming pool contains… 9,403 gallons
One household’s annual water usage is… 94,900 gallons
One Olympic-size swimming pool contains… 660,000 gallons

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