IWRA Proceedings

Knowledge of the availability and use of water resources is essential for effective planning at national, state and local levels.  Several inventories and forecasts of water resources in the United States have been conducted over the past 50 years in order to provide this critical information (Landsberg, et al., 1963; Wollman and Bonem, 1971; National Water Commission, 1973; Water Resources Council, 1968, 1978; and Brown, 2000).  Researchers from diverse disciplines have described the influence of factors such as climate, price, markets, and technology on water use.  These efforts have substantially improved our understanding of the role of water and other natural resources in the Nation’s welfare and economic development.

In the US a unique program to estimate water use began with a 1950 report prepared by the USGS (MacKichan, 1951).  This report ultimately served as a template for the nine reports that followed, which provided updates of water use estimates in 5-year increments (MacKichan, 1957; MacKichan and Kammerer, 1961; Murray, 1968; Murray and Reeves, 1972 and 1977; Solley et al., 1983, 1988, 1993, and 1998). In 1978 Congress acknowledged the value of the program by appropriating funds to establish the National Water Use Inventory Program (NWUIP), a co-operative federal-state effort to collect and store water use data.  This commitment of funds and staff time permitted the NWUIP to focus on improved quality in data collection procedures and to provide water-use information at increasingly detailed levels.  Several publications provide a review of the history of the changes in the USGS water-use program (Lumia, 2000; NRC, 2002).  In general, the USGS estimates of water use have focused on annual total water withdrawals, which include the extractions of both fresh water and saline water, with separate estimates of withdrawals from surface water and groundwater sources.  These estimates are based upon the aggregation of point withdrawals for various water uses reported at the state level, and since 1985, also at the county level.  Although the structure of the water use inventories has changed over time, in general, eight categories (or sectors) of water use are specified: public supply, commercial, industrial, irrigation, thermoelectric generation, self-supplied domestic, livestock, and
mining.  (Estimates of in-stream water uses are also included but these are not discussed in this paper.)  

A review of the changes in estimated water withdrawals has been a routine part of the USGS inventory circulars since the second national report in 1955.  In the most recent water use circular, Solley, et al. (1998, p. 63) provide a comprehensive review of the estimates collected from the entire series of water use inventories.
The analysis presented in this paper combines this summary review of USGS water-use estimates with
demographic and economic data from the Census and other sources.  The purpose of this paper is to provide
insight into changing trends in water use, the factors that influence water use, and the changing relationship
between water withdrawals and these factors.  The method developed in this paper to examine the influences on
past water withdrawals is also used to assess the influence of projected trends in explanatory variables on future
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