Water “lost” by infiltration into the land and losing stream beds does not simply vanish, and water that flows from springs and seeps does not simply appear. Physics governing the flow of water (based on hydraulic head representing the energy per unit weight of water and the principle of mass conservation) “connects the dots” so we know the continuously moving, albeit slow, groundwater flow in the unviewable subsurface, is an integral part of, and the anchor for, the terrestrial portion of the global water cycle (Figure 72).
The Earth’s population of nearly 8 billion in 2020 is expected to reach 11 billion by 2100. Humans will have to learn to produce sufficient food without destroying the soil, water and climate. This has been called the greatest challenge humanity has faced (Bourne, 2015). Sustainable management of groundwater is at the heart of the solution. Scientific understanding and proper management of groundwater is essential, because groundwater can alleviate the problem if we seek its responsible use and replenishment through better governance.