Kathleen Ferris of the Arizona Municipal Water Users Association on the difficulty of comparative water use analysis:
[C]omprehensive information on conservation and reuse implemented to date is not available. Each of the water providers within the ten metropolitan areas track information about their conservation programs differently. For example, water use in central Arizona is tracked by the state Department of Water Resources based on reports that cities are required to file annually. We have been collecting that data for over 30 years. Most metro areas track their information separately. On top of this, there are no consistent accounting categories or definitions and that makes comparing efforts virtually impossible.
Having wrestled with this problem myself, I “+1” Ferris’s observation.