William M. Alley and Rosemarie Alley—

Groundwater is the source of drinking water for about half the world’s people, as well as the dominant source of household water in rural areas. Many large cities depend solely or largely on groundwater. Groundwater is also critical to food production, providing more than 40% of irrigation water worldwide. Its importance is increasing, as the world may need to double global food production in coming decades to feed nine billion or more people. New crop varieties, improved agricultural practices, reduced food waste, and leaner diets can all help meet this goal, but groundwater is essential. It is also our best insurance against droughts. Meanwhile, many aquifers throughout the world are under stress and face an uncertain future.

The challenges of getting people to recognize the seriousness of groundwater problems are not unlike those associated with climate change. It’s hard to appreciate the scope of a problem you can’t see and that develops slowly. Our inability to see groundwater contributes to its lack of attention in water policy and management, as well as in agriculture, energy, the environment, land-use planning, and urban development. Groundwater has an important, but often forgotten, role in these sectors, and decisions within them affect how we use and manage groundwater.

Every groundwater situation is unique in its challenges. At one extreme is mining “fossil water” from aquifers having no, or minimal, present-day recharge. Examples include the southern High Plains in the U.S. and many aquifers in North Africa and the Middle East. For these systems, critical questions center on how much groundwater is economically recoverable, what are the appropriate rates of depletion, and how does society make a “smooth landing” from excessive groundwater dependence. These questions are rarely addressed in any serious way.

At the other end of the spectrum are aquifers in geologic and climatic settings where groundwater pumping can be indefinitely maintained. Withdrawals during dry periods are balanced by replenishment during wet periods. However, many of these aquifers are shallow and are particularly vulnerable to contamination. In these situations, protecting groundwater quality is of paramount concern.

Many, if not most, groundwater systems fall somewhere between these two extremes. These aquifers are naturally replenished, but are vulnerable to excessive groundwater withdrawals. Often, only a small part of the total groundwater in storage can be used without significant effects on surface water, ecosystems, land subsidence, or water quality. It is these groundwater systems where the concept of groundwater sustainability typically arises. While easy to say and seemingly self-evident, groundwater sustainability is among the hardest of goals to achieve. Achieving this goal requires a trade-off between today’s use and the future impacts of that use.

The effects of pumping on groundwater depletion, land subsidence, water quality, surface water, and ecosystems are at a tipping point for many of the world’s most critical aquifers. Solving these problems on a societal level involves more than just understanding the facts. People’s emotional values about the environment, views on current and intergenerational equity, and local customs complicate the question of what impacts are acceptable. Within this complex mix of competing interests, scientists are increasingly challenged to become socially sensitive team players.

Managing groundwater resources sustainably requires thinking on a different timescale. The response time of rivers, lakes, wetlands, and springs to groundwater pumping can be many decades, yet groundwater planning horizons (when they exist) are often only five to twenty years. Some groundwater planning horizons are now looking at fifty or even 100 years, but these longer time frames typically involve deliberate depletion of the resource. Antiquated groundwater laws and policies also need to be updated to reflect the dynamic interconnection of surface water and groundwater.

While safeguarding groundwater is a global challenge, most solutions are found at the aquifer, watershed, or local level. An external force is often required to achieve necessary changes and accountability, but top-down management usually sets up resistance among stakeholders. There is virtually no possibility of getting entrenched groundwater users on board if they aren’t actively involved in the decision-making process.

Successful long-term management of groundwater resources requires ongoing data collection and sustained funding by government agencies with sufficient resources and expertise. Data collected over a period of decades are needed to monitor the effects of aquifer development and track long-term trends. Unfortunately, political and financial support for even the most basic data collection is usually a low priority. Cutbacks to environmental funding promised by the Trump administration are alarming not just in terms of basic environmental safeguards but also resource monitoring and assessment.

Groundwater is simultaneously a vast, a limited, and a threatened resource. Virtually all of the world’s most pressing environmental problems require cooperation and collective action. Groundwater is no exception.

Director of science and technology for the National Ground Water Association, William M. Alley is a hydrology expert and authority on groundwater. Rosemarie Alley is a veteran science writer. They previously coauthored the book Too Hot to Touch, on nuclear waste.

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