The U.S. Geological Survey (USGS) has estimated the use of water in the United States at 5-year intervals since 1950. This report describes the water-use categories and data elements required for the 2005 national water-use compilation conducted as part of the USGS National Water Use Information Program. The report identifies sources of water-use information, provides standard methods and techniques for estimating water use at the county level, and outlines steps for preparing documentation for the United States, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands. As part of this USGS program to document water use on a national scale for the year 2005, estimates of water withdrawals for the categories of public supply, self-supplied domestic, industrial, irrigation, and thermoelectric power at the county level are prepared for each State using the guidelines in this report. Estimates of water withdrawals for aquaculture, livestock, and mining are prepared for each State using a county-based national model, although study chiefs in each State have the option of producing independent county estimates of water withdrawals for these categories. Estimates of deliveries of water from public supplies for domestic use by county also will be prepared for each State for 2005. As a result, domestic water use can be determined for each State by combining self-supplied domestic withdrawals and publicly supplied domestic deliveries. Fresh ground-water and surfacewater estimates will be prepared for all categories of use; and saline ground-water and surface-water estimates by county will be prepared for the categories of public supply, industrial, and thermoelectric power. Power production for thermoelectric power will be compiled for 2005. If data are available, reclaimed wastewater use will be compiled for the industrial and irrigation categories. Optional water-use categories are commercial, hydroelectric power, and wastewater treatment. Optional data elements are public-supply deliveries to commercial, industrial, and thermoelectric-power users; consumptive use; irrigation conveyance loss; and number of facilities. Aggregation of water-use data by eight-digit hydrologic cataloging unit and by principal aquifer also is optional. Water-use data compiled by the States will be stored in the USGS Aggregate Water-Use Data System (AWUDS). This database is a comprehensive aggregated database designed to store both mandatory and optional data elements. AWUDS contains several routines that can be used for quality assurance and quality control of the data, and produces tables of wateruse data compiled for 1985, 1990, 1995, and 2000.