What is groundwater?
Groundwater is water found underground in aquifers – rocks, sands and gravels that hold large quantities of water. It feeds springs, rivers, lakes and wetlands, and seeps into our oceans and can be extracted to the surface by pumps and wells. Rain and melting snow seep into the ground and help to replenish the store of groundwater.
Almost all the liquid freshwater in the world is groundwater – life would not be possible without it. Groundwater supplies much of the water we use for drinking, sanitation and agriculture. It supports ecosystems, such as wetlands and rivers. In some places though, human activities pollute groundwater, making it unusable. Over-exploitation of groundwater can lead to land instability and subsidence, and, in coastal regions, to sea water intrusion under the land.
Groundwater is out of sight but its impact is visible everywhere and it is everywhere under our feet. As Prof David Kreamer, President of the International Association of Hydrogeologists, asserts, “If earth has a hidden underground pulse, that pulse is groundwater.”
In the driest parts of the world, groundwater may be the only water people have. Closer to home it provides about one-third of public water supplies in England and Wales, 6% in Northern Ireland and 3% in Scotland.
Groundwater keeps our rivers flowing throughout the year, even in times with no rainfall, through springs and seepage. Chalk streams are well-known examples, as campaigners like Feargal Sharkey have highlighted. River water can disappear into the ground and reappear far away, having travelled underground through cave systems.
When we take water from rivers for water supply, agriculture and industry, a large proportion of this is actually groundwater. Groundwater maintains nationally important wetlands across the country, often giving rise to distinctive ecosystems dependent on the natural quality of the groundwater. There are even small creatures that live in groundwater in cave systems.
We import vast quantities of water – not just bottled mineral water but also an estimated two-thirds of all the water that the UK needs, which comes embedded in imported food, clothes and industrial goods. Much of this is groundwater. In a changing climate, this can exacerbate problems that countries may have in managing their water and growing food for themselves.