Those who work in municipal water departments or follow trends in domestic water use have been noting for several years that household water use has been trending downwards, for much of the past 20 years. The chart below shows percentage change in water usage per service connection for three different types of users in the Tucson Water system from 1997 to 2007.
During a multi-year study designed to establish a roadmap for developing sustainable water policies for the region, one of the recommendations was to take a hard look at data on residential water use and try to determine why this trend was occurring.
Just this past week, staff from Tucson Water and Pima County Flood Control released the results of that study in a data-intensive report that is available here (link will download the pdf file). This is an incredibly important report for future water planning efforts in this region. It's also applicable to many other regions, because the trend described above is not unique to Tucson - it's showing up all over the place.
I highly recommend checking out the report if this sort of thing appeals to you.