9
Conclusions and Recommendations
The National Water-Use Information Program (NWUIP) is responsible for the collection and dissemination of data on the use of water resources within the United States. This is the nation’s only assessment of such data. As the nation’s source of unbiased science-based information on water resources, the U.S. Geological Survey (USGS) is uniquely qualified to compile and provide water use information. This information is essential to the nation to maintain a national water inventory, assure the nation’s water supply, evaluate whether water supplies are sufficient for current and future needs, and evaluate the quality and quantity of water available for ecological resources.
The NWUIP is different from other water resources programs of the USGS. It is the only USGS water resources program in which the USGS does not have the principal responsibility for primary data collection. Instead, the USGS generally compiles existing data from other federal, state, and local sources. The quality of these data, therefore, is highly variable and depends upon the interests of the state or local cooperators. For this reason there are significant differences among USGS districts in data collection and/or estimation procedures, quality assessment procedures, and data distribution and accessibility. Financial support for the NWUIP largely comes from the USGS Cooperative Water (Coop) Program, whose funds are generally unavailable in states making little effort to collect water use data. This makes it difficult for USGS district offices in states not providing matching funds to compile their state’s information for the five-year national water use summary reports (a key product of the NWUIP). These reports, “Estimated Water Use in the United States,” have been published every five years since 1950 and are one of the most widely cited publications of the USGS.
Water use data are collected at various spatial scales: for political units such as counties and states and for water resources units such as river basins, aquifers, and hydrologic units. The merit of using political units is that ancillary information on population and economic variables is readily available for them if indirect estimates of water use are needed. The merit of using water resources units is that water use can readily be linked to water availability and to the annual water budget. Where available, site-specific water use data can be summed over any required geographic area to create aggregated water use estimates.
The USGS collects water use data for a set of water use categories, and it differentiates the use of surface water from groundwater. The water use categories include public water supply, industrial and commercial use, irrigation, livestock and domestic use, and, in some states, other water uses such as aquaculture and mining. Of these categories, the most systematic data are available for public water supply. Local water utilities maintain extensive records of water pumping and household water use required for billing. Supplemental data (including population served, source waters, and treatment processes) are available for every public water supply system through the U.S. Environmental Protection Agency (EPA) Safe Drinking Water Information System.
Industrial and commercial water use data are less systematically collected across the nation, although some states maintain comprehensive inventories of these data. Irrigation water use data are highly variable in quality, depending on reporting requirements at the level of the state, the watershed, or the irrigation project. Livestock and rural domestic water use involves small amounts of water that often fall below the trigger levels used in state water use data collection programs. No states routinely collect, or require reporting of, instream water needs or ecological water requirements, even in regions where such ecological estimates of water use are used in water resource allocation decisions.
With assistance from the NWUIP, the committee surveyed water use data collection practices for all 50 states, Puerto Rico, and the District of Columbia. This survey showed that most states collect water use data annually, if at all, but about 10 states maintain a comprehensive site-specific water use database of monthly water use data. Monthly data are valuable because they quantify the seasonal variability of water use, especially for irrigated agriculture, and they support monthly computation of the hydrologic water balance in watersheds and river basins. A more comprehensive survey and analysis of state water use data collection programs would be very valuable and would have many useful applications.
The committee’s examination of NWUIP data suggests that statistical sampling and estimation methods can be applied to derive water use estimates for different spatial scales, such as states, counties, river basins, aquifers, and hydrologic units. In one case study, the committee examined data on irrigation withdrawals in Arkansas, a state with a “complete” inventory of many water use categories, to investigate the standard error in state-level estimates that would
have been achieved by stratified random sampling of a small percentage of permitted withdrawals. The results of these preliminary investigations were very encouraging. They suggest real potential for the NWUIP to make greater use of statistical sampling to obtain water use estimates for states that, unlike Arkansas, do not do a complete inventory. Study of data from other states would, of course, be needed to refine appropriate sampling strategies.
In another case study, the committee analyzed the structure of the 1980–1995 state-level data from the NWUIP by multiple regression analysis in order to determine if aggregate water use could be correlated with routinely collected demographic, economic, and climatic data. Indeed, a number of potential explanatory variables for water use were identified for several major water withdrawal categories. These included water price and gross state product for public water supply, and the existence of “closed-loop” systems (i.e., cooling towers) for thermoelectric withdrawals. Significantly, the analysis also found discernable responses to climate variability in aggregate state-level data. This suggests the feasibility of normalizing water use estimates for interannual climate variability using statistical techniques.
These analyses suggest how statistical methods may yield rigorous estimates and quantitative confidence limits for aggregate water use. Where such an inventory is cost-effective, water use estimates should be based on a complete inventory of significant water use sites in a region. In practice, water use estimates compiled for each category and county in the nation will consist of a combination of direct observation, random sampling, modeling, and statistical estimation. This mixture of water use estimation techniques requires a framework that best combines data from direct inventories with estimates from statistical sampling and modeling. In this framework, the NWUIP would be supported by water use data, water use estimation, and integrative water use science.
The integrative science that is needed to complement the data and estimation methods described above is rarely done. Consequences of water use practices have been a focus of several new National Water-Quality Assessment (NAWQA) studies, illustrating the potential utility of integrating water quality, quantity, and use. However, water use data are usually not a major component of scientific studies conducted by the USGS. The minimal level of integration of water use data into USGS hydrologic studies is not healthy for the USGS or the nation.
The committee also found significant potential for the NWUIP to coordinate its data collection efforts more closely with activities of other agencies and institutions in order to integrate national databases in the NWUIP. The USDA maintains a five-year Census of Agriculture, which inventories irrigated agriculture using a stratified random sampling approach similar to that suggested in this report for water use. The EPA maintains a Safe Drinking Water Information System and a Permit Compliance System, both of which contain valuable inventories of water-using facilities. The Energy Information Administration maintains detailed operating information on the nation’s power plants that may be
useful for estimating thermoelectric water use. Site-specific water use datasets compiled at the state level also provide a rich store of information. Integrating these state and national databases will support the rigorous systematic evaluation of water use sampling and estimation methods recommended by the committee.
RECOMMENDATIONS
Many recommendations for improving the NWUIP are found within the individual chapters of this report. Of these, there are five comprehensive recommendations that will lead to a more scientifically based and better-integrated water use program. These recommendations are summarized in the following paragraphs.
Create a Water Use Science Program
The NWUIP appears to be viewed as a water use accounting program by many scientists in the USGS Water Resources Division. NWUIP needs to be elevated to being an integral part of the scientific data collection and dissemination mission of the agency. The program would significantly benefit from rigorous, hypothesis-driven research to improve our knowledge and understanding of the role of water use in hydrologic and hydrogeochemical processes and to enable the systematic development of rigorous statistical techniques for national water use estimation. Because of the significant differences in water use data collection procedures and data quality from state to state, water use accounting alone cannot provide the estimates of water use that are needed by the nation.
Rather, integrative water use science will require a more complete data paradigm, capable of tracking the sources and fate of water, as it flows between the infrastructure and natural water systems. A “link-node” representation of the movement of water from points of withdrawal, through the infrastructure water system, to points of water discharge, and back to the natural water system is one useful approach. This comprehensive and integrated approach creates the data structures and framework needed to track changes in both water quantity and quality as water moves through the landscape.
The intimate linkage between water quality and water quantity creates both opportunity and need for better connections and integration between the NWUIP, the NAWQA Program, and the USGS Biological Resources Division (BRD). Water requirements for ecological uses of instream water compete with water withdrawals from streams for other uses. In integrative water use science, both withdrawal uses and instream uses are logically parts of the total water use, within which the effects of human water uses on ecological resources can be studied. The linkage of water use infrastructure with natural water systems offers a robust framework for understanding the impacts of water use on water quality,
on aquatic ecosystems, on the hydrologic cycle, and on the reliability and vulnerability of the nation’s water resources.
Recommendation: The NWUIP should be elevated to a water use science program, emphasizing applied research and techniques development in the statistical estimation of water use and the determinants and impacts of water-using behaviors.
Improve the Water Use Database
The current water use program does not have a systematic approach to evaluating the accuracy of water use data. Although the quality of the NWUIP’s historical data can be improved with consistency checks, with analysis of model residuals, and with other quality assurance techniques, the resultant data sets will not be error-free. The highest-quality water use data will come from comprehensive data collection programs that field-verify primary water use data collected at sample sites.
The committee’s survey of existing water use datasets has revealed that about 20 states have comprehensive site-specific databases of annual water use, and most other states have water use data for some water use categories. In addition, the federal government systematically collects information about water use facilities just as it collects national economic, population, and other resource data relevant to water use estimation. These data can be integrated and synthesized at the national level to systematically support more rigorous water use science in the United States. The convergence of consistent national data sets and widely available standard technologies in geographic information systems creates a timely opportunity for USGS to improve the acquisition and management of data used to estimate national water use.
Recommendation: To better support water use science, the USGS should build on existing data collection efforts to systematically integrate datasets, including those maintained by other federal and state agencies, within the data collection and water use estimation activities of the NWIUP.
Improve Water Use Estimation with Improved Statistical Procedures
National summaries of water use are produced every five years by the USGS using an inventory approach in which an estimate is made of the total water use in each of a set of water use categories for each county in a state. The state totals are then summed to create national totals. To the extent possible, county and state estimates are based on information from surveys of water users, supplemented by indirect estimates where surveyed water use data are not available. Statistical investigations carried out by the committee suggest the potential for improve-
ment that could be realized from conducting the estimation of state and national water use through a rigorous framework of statistical sampling and estimation. Research on statistical estimation of water use should include a systematic evaluation of the errors of reported and measured major water uses. This would strongly complement the USGS’s expertise and activities in other national statistical synthesis efforts such as the NAWQA Program.
Recommendation: The USGS should systematically compare water use estimation methods to identify the techniques best suited to the requirements and limitations of the NWUIP. One goal of this comparison should be to determine the standard error for every water use estimate.
Integrate Water Use Information into USGS Water Resources Research Programs
Human use of water is highly dependent upon the availability of water, which is susceptible to climate change. Human water use is one of the main mechanisms changing the spatial and temporal distribution of the natural water resource system. Water use should be viewed as a component of the hydrologic budget for watersheds, aquifers, and river basins. Water use estimates should be used to assess the impact of human activity on the quantity and quality of water within the hydrologic systems of interest. Water use data can be used to evaluate water use trends and to estimate future water needs in river basins or aquifers where water resources might be limited.
An integrative water use science program that investigates spatial and temporal patterns of water use, impacts of water use on aquatic ecosystems and the hydrologic cycle, and the sustainability, reliability, and vulnerability of water resources cannot stand alone. It needs to leverage the resources of other USGS programs. An example would be an investigation of the feasibility of modeling approaches (such as adaptations of the water-quality model SPARROW) to assess the relevance of water and land use information in determining water availability. Another example is developing a framework for incorporating estimates of instream flow used for ecological purposes. Collaboration with the Biological Resources Division and with state and federal resource management agencies will be necessary to develop such approaches.
Recommendation: The USGS should focus on the scientific integration of water use, water flow, and water quality in order to expand knowledge and generate policy-relevant information about human impacts on both water and ecological resources.
Redefine the Goals of the Water Use Program and Improve the Status of the Program Within the USGS
In this evaluation of the NWUIP, the committee found a program that is a unique source of critically needed water use data for the nation and for other water resources programs within the USGS. This report envisions a substantial transformation of the NWUIP. The committee does not see the NWUIP as simply a database management program focused on county-level categorical water use. Rather, the committee finds a natural role for the NWUIP to complement and become actively integrated with the Survey’s other efforts to provide unbiased science-based information about the nation’s water resources. This focus requires a core national effort to supplement the activities presently carried out by the water use programs in the states.
The USGS must find a stable source of dedicated funds to support a continuous, sustained effort to collect, analyze, evaluate, and disseminate water use data. The sole reliance on Coop Program funds has resulted in a national program that is based on data collection procedures with variable regional coverage and weak control of the quality of the data. This is inconsistent with the Survey’s role as the nation’s unbiased source of water resources information.
Recommendation: The USGS should seek support from Congress for dedicated funding of a national component of the recommended water use science program. This funding would supplement the existing funding in the Coop Program.
