Opinion: Groundwater: out of sight, out of mind?

groundwater - On World Water Day Professor Richard Taylor (UCL Geography) and Dr. Mohammad Shamsudduha (UCL IRDR) explore equitable and sustainable use of groundwater. Today is World Water Day. Despite the centrality of water in our everyday lives and life itself, we often mark this day not by reminding ourselves of all that water brings but of the consequences of its absence or contamination. Today, hundreds of millions of people around the world still do not have access to basic water services and, in England, every river is too polluted to support its ecology or  officially  fit for swimming. As the American polymath Benjamin Franklin noted, " when the well runs dry, we (shall) know the worth of water. " This direct reference to groundwater, the water flowing through the pores and cracks in rocks beneath our feet, is fitting as the theme of World Water Day 2022 is  Groundwater: Making the Invisible, Visible. Groundwater differs from the water running off into rivers, lakes and wetlands as this underground flow derives from the infiltration of precipitation that has occurred over periods ranging from years to decades and, in places, millennia. Much of the estimated ~23 million km3 of groundwater in the upper 2 km of the Earth's crust is ancient, yet the shallower component of groundwater replenished over the last half-century still greatly exceeds all other unfrozen freshwater on Earth. As the world's largest distributed store of freshwater, groundwater plays a vital role in not only sustaining aquatic ecosystems during periods of low or absent rainfall but also providing access to safe water, especially to off-grid communities. In drylands stretching across ~40% of world's land area, groundwater is often the only perennial source of freshwater.