A century of activity and publication of more than 860 water-resources related reports for the State of Arizona demonstrate an historical role for the U.S. Geological Survey in the hydrologic community. These reports continue to serve as the foundation of hydrologic knowledge for the State. Additionally, hydrologic historians will note (1) the evolution and sophistication of the investigative and interpretive tools used to collect and transfer hydrologic data knowledge to the water-user community and (2) a strong and steadfast nonregulatory stance in the midst of highly controversial and political issues. The justification for this stance is simple the need has existed and will continue to exist for an unbiased entity such as the U.S. Geological Survey to produce credible scientific information. Major national water issues for the Water Resources Division during fiscal years 1986-91 correspond well to water issues in the State of Arizona. These issues are (1) water availability and competition for this water, (2) quality of water, and (3) management of water and land resources. Studies being conducted by the U.S. Geological Survey and described in this publication are, for the most part, in support of providing data and interpretation to address these issues. As an agency, we are aware of and dedicated to the premise that credible data are obtained only when subjected to consistent, discipline-related, quality-assurance programs. Throughout the Water Resources Division, continuous quality-assurance programs are conducted for all the activities that influence and ensure the quality of our products and services. Relevant and complex studies conducted by the Arizona District include radionuclide contamination in the Puerco River basin and migration of acid mine drainage in the Final Creek basin in central Arizona. In the lower Colorado River basin, a new method of estimating and distributing consumptive uses of Colorado River water for each user has been developed and work is underway to refine and improve the new method. Looking to the future, the Arizona District is seeking opportunities to develop a means of quickly and economically tracking changes in the quantities of ground water in storage. The use of sensitive gravity meters has shown great promise and when developed could greatly reduce the cost and time of using water-level measurements in individual wells. In a situation where "safe yield" is a management objective, this new method could be a valuable tool. With regard to groundwater contamination, we are seeking opportunities to evaluate the effectiveness of developing technologies in bio-remediation. The present use of "pump and treat" is proving extraordinarily expensive and of limited effectiveness. Another topic of interest is in monitoring and simulation modeling of land subsidence resulting from groundwater withdrawals. In areas where subsidence has been significant, the effects on the operation and integrity of water distribution and drainage systems have been substantial and expensive. Predictive...