The Toilet Comparison Calculator is designed to compare the water, energy and carbon costs of toilets with different water efficiency ratings. Because toilets use only cold water, this tool is particularly useful for helping people understand the indirect – or upstream and downstream – energy and greenhouse gas emissions embedded in their water use.

After selecting the appropriate state, users then select the gallons per flush of their toilet based on the year the toilet was installed or manufactured. Users then provide information on the number of people in their household and the number of times each person flushes the toilet in a typical day. The final two inputs are the energy intensity of the local water supply system and wastewater treatment system, respectively. Although national averages are provided, users are encouraged to contact their local water and wastewater utilities to determine the energy intensity of their water systems, since these are the primary factors influencing the energy and greenhouse gas emissions embedded in the water used for toilet flushing.

To use this tool, data is entered on the left-hand side of the screen and the results display to the right of the white divider line. The data and assumptions behind this tool can be viewed by clicking on the “Assumptions” tab in the bottom left corner of the workbook. Please note that these models are designed for educational purposes and are not intended to provide a comprehensive analysis of a given scenario.