The theme for this third publication of the UNESCO i-WSSM Global Water Security Issues is the role of sound groundwater resources management and governance to achieve water security. As an underground resource, often called the invisible resource, groundwater is more difficult to quantify, assess and monitor than surface water resources. In addition, the general public and many decision-makers are often not aware of the need for careful management of groundwater resources, or the best practices to steward these resources for current and future generations. When groundwater is withdrawn faster than an aquifer can recharge, many problems can arise, such as ground subsidence and water quality deterioration. Also, when water withdrawal exceeds water recharge, aquifers are no longer sustainable resources. Further, some aquifers were formed many thousands, or even millions, of years ago and the climatic conditions that created them no longer exist, so these aquifers do not refill when water is withdrawn. Water withdrawn from aquifers that do not recharge results in the depletion of a non-renewable resource. Gaps in mapping and quantification of aquifer resources compound the multiple challenges of managing an underground resource. Climate change will affect, and is already affecting, natural conditions that influence groundwater, such as soil moisture, evaporation rates, spatial and temporal precipitation patterns, recharge rates, and chemical processes (such as oxidation and reduction reactions) that influence water quality, water quantity and seasonal water availability.
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