Communities in many parts of the world are facing increasing difficulties in obtaining a
sustainable, long-term supply of freshwater in the face of increasing populations and, perhaps,
also global climate change. Aquifer storage and recovery (ASR) is increasingly being looked
upon to provide large volumes of storage to capture seasonally or intermittently available excess
water for later beneficial use. ASR is a proven technology, but its implementation has not been
free of problems. ASR systems vary in their hydrologic value (i.e., the degree to which they
achieve useful storage) and, in some instances, have either not met expectations or have failed
entirely. It is now clear that the hydrogeology of ASR systems, such as the effects of aquifer
heterogeneity and water-rock interactions, are more complex than originally envisioned.
Excessive regulatory requirements unnecessarily increase project costs and adversely impact the
economic viability of projects. However, the advantages of ASR as a tool for water resources
management are still compelling. The challenge moving forward is to take advantage of the
lessons learned from the recent explosive growth in ASR system construction and research in
order to improve upon all aspects of the implementation and regulation of ASR. Includes 21 references, figures.