Competition for water will increase in the twenty-first century as we strive to meet the demands resulting from continued population and economic growth, and from efforts to protect and enhance aquatic ecosystems. Anticipated changes in the hydrologic cycle and hydrologic variability caused by global climate changes, the public's growing disaffection with dams, and the fact that virtually all surface waters are fully allocated, strongly suggests that groundwater will be an increasingly important component of water supplies in the future. The fact that groundwater, accounts for two-thirds of the freshwater resources of the world, and that its long residence time serves to protect it from short-term contamination problems, should instill confidence that it will be available to meet future agricultural, domestic, and industrial needs. However, large-scale groundwater development throughout the nation has resulted in many ill effects, including lowering of water tables, salt-water intrusion, subsidence, and lowered baseflow of streams. The burgeoning examples of local and regional groundwater overdrafts, and point source and nonpoint source contamination from planned and inadvertent actions, call into question the sustainability of this resource.

In the face of the concern about the depletion of groundwater reserves, thousands of aquifer recharge wells and aquifer storage and recovery (ASR) wells, and innumerable recharge basins, have been constructed to replenish water in aquifers. Such efforts are generally intended to prevent saltwater intrusion and land subsidence, and maintain baseflow in streams. The ASR wells are specifically intended to augment drinking water supplies. Most ASR wells being used today recharge drinking water. Changes in water quality during storage have proven to be minimal so that disinfection is the only treatment required on recovery. Thus, it appears that the use of ASR wells to inexpensively store drinking water underground in order to provide a secure community water supply for several months is an option that many water managers would probably support. The principal need with regard to the recharge of drinking water is to develop guidance for ASR legislation and regulations, possibly a model ASR code, so that issues and regulatory experiences in states with operating ASR systems are more readily available to those states that may wish to develop their own ASR regulatory framework.

Expanding ASR to store and recover treated surface water, untreated groundwater or treated waste water would serve to conserve waters that would ultimately go unused. However, such groundwater augmentation efforts are currently being resisted. Legislation authorizing the use of non-drinking water for ASR recharge has been blocked in several states at least in part due to concerns about aquifer contamination and human health. Current federal regulations requiring that recharge waters meet all primary drinking water standards at the wellhead prior to recharge also may make it prohibitively expensive to recharge anything but potable water. Acceptance of this potentially important source of drinking water requires answers to many technical, economic, and regulatory questions.

For instance:

• What type and degree of treatment is necessary to ensure that no pathogens will survive in groundwater? Will disinfection lead to the formation of carcinogenic compounds that will move to broader groundwater areas?
  
• What information is needed to ensure that the water being recharged is geochemically and microbiologically "compatible" with native groundwater? Unanticipated reactions may lead to poor-quality water, biomass formation, pathogen growth, and well clogging.
• What are the energy costs associated with ASR?
• What monitoring will be required to ensure that unforeseen water-quality problems do not affect broader groundwater resources?
• How will communities be assured that the recharged water will not adversely affect other aquifers or surface water bodies?
• What are the economic benefits that are to be expected from ASR? Maintaining high baseflow that supports ecosystem function, for instance, may be viewed as an important indirect outcome of ASR. Likewise, higher baseflow from ASR may increase dilution of surface-water contamination and bring into compliance stream reaches that may otherwise exceed Total Maximum Daily Load requirements.
• What scale of ASR is technically and economically feasible?
• What are the impacts of ASR on property values? On land use patterns?
• What are the regulatory barriers to ASR?
• What alternatives exist to augment drinking supplies?
• How do they compare with ASR?

The need exists for leadership by those in the water management community to answer these, and other, technical, economic, and regulatory questions and disseminate the information to the public, water managers and regulators. Federal laws and regulations must be reviewed to ensure that they reflect the state of knowledge about the risks and benefits of ASR.

The answer to such questions requires an analysis of the direct and indirect benefits and risks of ASR. The analysis would transcend traditional approaches by recognizing that water is to be valued not only for its extractive worth but also for its "in-situ" worth, a worth based on the essential role water plays in supporting life and ecosystem function. The analysis would take into consideration the role ASR plays in water management during times of floods and drought and as a strategic source of supply during regional or national emergencies.

The purpose of this evaluation is to provide policymakers, regulators, and water managers an objective summary of the technical, ecological, and economic factors that affect the efficacy of ASR and the options for its implementation. The initiative would use case studies to determine actual examples of benefits and risk.