Life on Earth depends on water, especially fresh water, and without it we would not be here. Groundwater is an essential reservoir of fresh usable water that we can tap into when rain or surface water are not plentiful enough. A quarter of the world’s population depends on the fresh water that is stored in underground water stores, or aquifers.
About three-quarters of the world’s fresh water stores are locked up in the polar ice-caps and glaciers, and about 15% is in very deep aquifers that are inaccessible. The rest is available to us as lakes, rivers, soil moisture and shallow groundwater, and is continually cycling through the land, the atmosphere and the oceans. Some of the groundwater is stored for long periods of time, however, sometimes for many thousands of years. It is not necessarily static, or stagnant though, it flows through permeable rocks and between layers of harder rock, much like an underground river, and is kept fresh by a kind of filtration system. Many rivers are kept flowing by a constant source of groundwater.
A good example is right in the centre of the United States, where half-mile wide, circular agricultural plots are found on the otherwise dry and dusty prairies. These plots are producing some of the world’s finest wheat, fed on water that is drawn from a huge underground aquifer that started out as melt-water from glaciers at the end of the last ice age. Water extraction began in the 1960s, and now 6 feet of water are extracted every year, but we must remember that these kinds of resources are not finite – only half an inch of water is replenished here per year by rainwater, and one day it will run out.
We must also take care about the purity of groundwater as water should be clean to drink. There is much evidence of nitrate pollution in groundwater, where unused fertiliser from fields seeps down into aquifers, and there can also be an accumulation of salts where the bedrock is impervious. In Bangladesh in the 1990s geoscientists discovered arsenic in the drinking water drawn from many of the wells that had been dug in a humanitarian effort to provide fresh drinking water to remote villages. Although the arsenic was a result of contamination from a natural chemical source, it has resulted in widespread chronic poisoning and high incidences of related cancers. This highlights the need for rigorous testing of groundwater if it is to be utilised in this way.
We may sometimes complain that it has been raining all week, but we should never take water for granted, it is our most valuable resource, and should be treated with respect and consideration for the future.