In recent summers, flows from the world's second-largest spring, the headwaters of the Al Khabour River in Syria, have declined from a long-term average of 50 cubic meters per second to only a few cubic meters per second. Similar stories are emerging in many regions. Groundwater-level declines of 1­3 meters per year are commonly reported for monitored wells in arid and semi-arid regions. In extreme situations, such as Sana'a in Yemen, shallow aquifers are almost depleted.

Efforts to tap new groundwater supplies in Sana'a have been unsuccessful despite the drilling of wells that exceed two kilometers in depth. In the Middle East and North Africa, it is no longer uncommon to encounter wells drilled to depths that have historically only been seen in the oil industry. Even in humid regions such as Bangladesh, water-level fluctuations may be increasing, and water is scarce during the dry season. Furthermore, scarcity and quality concerns are linked. Groundwater pumping often mobilizes water that is saline or contains natural contaminants such as arsenic or fluoride. When combined with increasing pollutant loads from agriculture, industry, and municipal sewage, this pumping can irreversibly contaminate aquifers.

The threats to groundwater resources are clear, but their extent is far less so. Worldwide, most groundwater monitoring networks are relatively new and collect a limited array of data on water levels and basic water quality parameters. Detailed data on water quality and pollutants are rarely available except in relation to specific local concerns. Data are also often unavailable on critical components of the water balance-such as groundwater extraction, evapotranspiration from native vegetation, and deep inflows to aquifers. Furthermore, data on water-level changes can be misleading. Aquifers can take tens to hundreds of years to equilibrate when disturbed. As a result, short-term waterlevel declines do not necessarily indicate overdraft.

Nonetheless, water-level changes and fluctuations are the most important factors influencing access to groundwater for the environment and for human uses. For small farmers along the Ganges, the deep saturated basin beneath their fields is irrelevant. What they care about is whether or not water is available within the tens-of-meters range from which they can afford to pump. When levels decline below or fluctuate outside that range, farmers lose access to irrigation and households may lose access to drinking water.

Fluctuations are equally important from an environmental perspective. Stream flows and wetlands often depend on high groundwater levels. Even modest seasonal declines can affect surface water bodies severely. Water quality is also affected when changing levels mobilize low-quality water or cause waterlogging and associated salinization problems. From the perspective of current usage, this dynamic-the interaction between groundwater levels, underground flow patterns, surface water bodies, and the economics of groundwater access-is far more important than the overall balance between extraction and recharge within an aquifer. Moreover, this dynamic is highly variable, heavily dependent on local conditions, and often missed in the data sets collected by groundwater departments.

Standard approaches to reducing groundwater overdraft, for example, often require metering of all wells, establishment of formal water rights, and regulatory and economic mechanisms to bring extraction down to sustainable levels. While progress toward this goal has been made in a few water-scarce countries such as Jordan and Israel, the situation is more complex in locations (such as India) with tens of millions of wells and conditions that vary greatly even at local levels. Even where management is most advanced, it is socially and politically difficult to reduce groundwater extraction to sustainable levels. Wells are generally private and highly dispersed. Inventorying them and monitoring extraction are problematic. Furthermore, reducing use to sustainable levels in arid regions often requires substantial reductions in extraction, which can have tremendous economic and social impact. As a result, governments are not inclined to force reductions.

Groundwater experts often propose community management of groundwater as an alternative to state regulation. Although global experience in this area is limited, experience with resources other than water indicates that several factors are critical to the success of community management-for example, clear boundaries on the resource and its user group, the ability to control free riders, and information on the use and condition of the resource. Such factors are difficult to establish in the case of groundwater.

Successful groundwater management has been achieved through intermediate-level institutions such as the quasigovernmental groundwater districts in the western United States and somewhat similar organizations in parts of France. Organizations of this type hold much promise. Their development, however, often takes decades, and to be effective they require data, technical capacity, and some degree of supporting social consensus.

Markets are also central to any framework for groundwater management. Water markets in the western United States are based on water rights systems that attempt to quantify the volume sustainably available in aquifers and allocate it among users. Transactions involve contracts and often the formal transfer of the water right as well as the water itself. In developing countries formal water rights are rarely involved. Instead, informal transactions occur between well owners and adjacent farmers for irrigation or tanker companies that deliver the water to urban customers. Prices for irrigation are low compared with tanker deliveries. In 1986 in Yemen, for example, the cost of extraction near Ta'iz was approximately US$0.005 per cubic meter. Rural irrigators paid US$0.02­0.05 per cubic meter; urban bulk users paid an average of US$2.60 per cubic meter for tanker supplies; and smaller customers paid as much as US$25.00 per cubic meter for purified groundwater. That pattern is typical: the urban poor generally pay the highest prices.

Two points merit attention. First, because formal rights are not involved, prices reflect short-term pumping capacity, not the longer-term sustainability of extraction rates. Second, even with rights systems, markets indicate the value individual users gain from extracting groundwater but not the economic, environmental, and sustainable use values that accrue when groundwater is left in place.

Aside from groundwater market prices, energy is the primary variable cost affecting groundwater extraction. In countries such as India, energy subsidies were used to encourage groundwater development during the Green Revolution. Now, despite water-level declines and huge effects on state budgets, those subsidies have proved politically difficult to eliminate. As a result, agriculture now officially consumes more than 50 percent of total power production in some Indian states. Appropriately structured energy prices can provide users with a major incentive to use groundwater more efficiently. Still, given the high yields associated with groundwater and the numerous factors affecting the economics of agriculture, energy prices alone cannot be expected to reduce groundwater extraction to sustainable levels.

For further information see Burke, J. and M. Moench. Groundwater and Society: Resources, Tensions, and Opportunities. New York: UN Department for Social and Economic Affairs and Institute for Social and Environmental Transition, 2000.; Foster, S., J. Chilton, M. Moench, F. Cardy, and M. Schifler. Groundwater in Rural Development: Facing the Challenges of Supply and Resource Sustainability. World Bank Technical Paper No. 463. Washington, D.C.: World Bank, 1999.; Foster, S., A. Lawrence, and B. Morris. Groundwater in Urban Development: Assessing Management Needs and Formulating Policy Strategies. World Bank Technical Paper No. 390. Washington, D.C.: World Bank, 1998.

Marcus Moench (mmoench@i-s-e-t.org) is president of the Institute for Social and Environmental Transition in Boulder, Colorado, U.S.A.