National Water Census
Through the Water Census, USGS will provide more comprehensive reporting of national information on withdrawal, conveyance, consumptive use, and return flow by sector of use. Water-use data enables water managers to plan more strategically and enables the analysis of trends of over time. It is also vital to water-availability studies such as watershed and groundwater models. The Water Census will build on a tradition of water-use reporting at USGS that dates back to 1950. The 5-year reports, titled Estimated Use of Water in the United States, are among the most cited information products produced by the agency and are produced in conjunction with datasets that can be downloaded and used by water managers nationwide. These reports can be accessed on the USGS Water Use program site).
The Water Census will adopt a comprehensive approach such as that used in the 1995 report (see History Page for more details). The report will include estimates of withdrawals, public-supply deliveries, wastewater returns, and consumptive use for 11 sectors (public supply, domestic, commercial, irrigation, livestock, aquaculture, industrial, mining, thermoelectric power, hydroelectric power, and wastewater treatment). In addition, the next Water-Use Report will return to an earlier practice (used in 1985, 1990, and 1995) of reporting water use by hydrologic units (at the HUC-8 level) as well as at the county level. Water-use data for counties is difficult to use for watershed-based water budgets. Reporting water-use estimates by hydrologic units in addition to counties will make it easier for end users of the reports to integrate the data into basin analyses and apply it to decision-making within the context of a broader watershed.
One of the major goals for improving water-use reporting is the need to refine the scale at which water-use information is reported. Finer scales of water-use data will improve water budgeting capabilities, and has the added benefit of allowing end users of the data to aggregate it to the scale of decision-making and customize their water budgeting. By working with the U.S. Environmental Protection Agency (EPA), USGS is developing a national Site-Specific Water-Use Database (SWUDS). The database will contain withdrawal, conveyance, use, and discharge information. Initially, this will be completed for the public supply sector. Withdrawal locations, conveyances, and water system information in SWUDS will be integrated with the National Hydrography Dataset (which tracks the 'natural' flows of water across the landscape). In the future, thermoelectric power plant locations and withdrawals will be added, followed by other sectors for which site-specific information can be developed. Detailed, long-term information on withdrawals, conveyances, consumptive use, and return flows will provide the critical demand component for studies of the interactions between human water use and the natural hydrologic system.
The Water Census also includes efforts to improve estimation methods for the two largest sectors of the Nation's water use: thermoelectric power and irrigation. These sectors account for a large amount of water used in the U.S., so better water-use estimates for these categories will increase the accuracy of water budgets overall.
Thermoelectric power accounted for almost half of U.S. withdrawals in 2005 (Kenny and others, 2009). However, significant amounts of the water withdrawn are returned to a surface-water body and are therefore readily available for other uses. Reports filed by power plant owners to the U.S. Energy Information Administration (EIA) are a major source of data for USGS thermoelectric power water-use estimates.
The USGS is developing improved estimation techniques for power plants utilizing data reported to the U.S. Energy Information Administration (EIA). The two agencies are working together to improve the quality and usefulness of the reported data. In the USGS study, power plants are divided into several classes on the basis of the level of data available for them, and estimation methods will incorporate information on plant characteristics, power generation, and fuel use to estimate a range of reasonable water demand. The results will help quality assure information on thermoelectric power water demands from various sources. The thermoelectric power study also will develop techniques for producing consumptive use estimates for power plants utilizing heat budget data. A retrospective study of estimates from 1975-1985 is examining factors which affect thermoelectric power water demand, such as cooling system type, fuel type, and weather conditions to better understand future changes in demand.
In 2005, water withdrawals for irrigation made up 31 percent of withdrawals. Compared to thermoelectric power, a larger proportion of the water withdrawn for irrigation is consumed through evapotranspiration or incorporated into the crop, leaving less available for immediate reuse. Estimating irrigation water use remains a challenge, and an analysis of the data and methods used for the 2000 and 2005 national estimates of irrigation water use (Dickens and others, 2011) resulted in recommendations for improving USGS future estimates. The study compared USGS irrigated-acreage estimates to acreage reported by the U.S. Department of Agriculture for similar years in order to assess the differences in magnitude and trends. The study also calculated a state irrigation withdrawal estimate by using an indirect method involving irrigated acreage, consumptive water requirement by crop, and potential water losses while irrigating. Estimates from the indirect method were compared to the published 2005 estimates in select States to evaluate the indirect method and provide a potential benchmark to quality assure future State irrigation estimates.
Under the Water Census, USGS is also developing improved methods for estimating quantities of water used for irrigation by estimating water that is conducted into the atmosphere through evapotranspiration. For more information on USGS Water Census research on evapotranspiration, visit the Evaporative Loss Page.
Kenny, J.F., Barber, N.L., Hutson, S.S., Linsey, K.S., Lovelace, J.K., and Maupin, M.A., 2009, Estimated use of water in the United States in 2005: U.S. Geological Survey Circular 1344, 52 p., available at http://pubs.usgs.gov/circ/1344/.
Dickens, J.M., Forbes, B.T., Cobean, D.S., and Tadayon, Saeid, 2011, Documentation of methods and inventory of irrigation data collected for the 2000 and 2005 U.S. Geological Survey Estimated use of water in the United States, comparison of USGS-compiled irrigation data to other sources, and recommendations for future compilations: U.S. Geological Survey Scientific Investigations Report 2011–5166, 60 p., available at http://pubs.usgs.gov/sir/2011/5166/.