With sections on:Water-resource development, By Onni J. Perala, U.S. Bureau of Reclamation; One of the great challenges faced by the Nation's water-resources scientists is providing reliable information to guide the management and protection of our water resources. That challenge is being addressed by Federal, State, Tribal, and local water-resources agencies and by academic institutions. Many of these organizations are collecting water-quality data for a host of purposes including: compliance with permits and water-supply standards; development of remediation plans for specific contamination problems; operational decisions on industrial, wastewater, and water-supply facilities; and research to advance our understanding of water-quality processes. In fact, during the past two decades, tens of billions of dollars have been spent on water-quality data-collection programs. Unfortunately, the utility of these data for present and future regional and national assessments is limited by such factors as the areal extent of the sampling network, the frequency of sample collection, the varied collection and analytical procedures, and the types of water-quality characteristics determined. Therefore, despite these expenditures, only a small part of the data collected can be used to assess the status, trends, and causes of water-quality conditions at regional and national scales.In order to address this deficiency, the Congress appropriated funds for the U.S. Geological Survey to begin testing and refining concepts in 1986 for a National Water-Quality Assessment (NAWQA) Program that, if fully implemented, would:1. provide a nationally consistent description of water-quality conditions for a large part of the Nation's water resources;2. define long-term trends (or lack of trends) in water quality; and 3. identify, describe, and explain, as possible, the major factors that affect observed water-quality conditions and trends.As presently envisioned, a full-scale NAWQA Program would be accomplished through investigations of a large set of major river basins and aquifer systems distributed throughout the Nation, which in aggregate, would account for a large percentage of the Nation's population and freshwater use. Each investigation would be conducted by a small team of individuals familiar with hydrologic system(s). Thus, the investigations would take full advantage of the region-specific knowledge of individuals in the areas under study. At present, four surface-water projects and three ground-water projects are being conducted as part of the pilot program to test and refine assessment methods and to help determine the need for and the feasibility of a full-scale program.iii The final interpretive results of the pilot NAWQA Program will be presented in a series of U.S. Geological Survey Water-Supply Papers. Each of the seven pilot projects will be described in a Water-Supply Paper with separate chapters assigned to key elements of each investigation. Chapter A will be reserved for a summary report. Chapter B will be an analysis...