Last edited 29 Mar 2019

Groundwater

The term 'groundwater' refers to all water which is below the surface of the ground and within the permanently saturated zone. A groundwater body is a distinct volume of groundwater within an aquifer. The term ‘hydrogeology’ refers to the nature, distribution and movement of groundwater in soils and rocks, including in aquifers. Ref The HS2 London-West Midlands Environmental Statement, Glossary of terms and list of abbreviations, DETR 2013.

Groundwater is an important part of the water cycle which continually moves water through the environment. Water evaporates from the oceans and condenses into clouds, before falling onto land as rain and flowing into rivers and back into the oceans.

However, the ground has the potential to interrupt this cycle, absorbing rainwater like a sponge. Some of this water will return to the atmosphere through processes such as transpiration, while some will infiltrate deeper into the ground where it becomes groundwater.

The water table is the level at which the ground becomes saturated and water will flow to a point of discharge such as a spring, lake, river or sea. Groundwater plays a vital role in supporting industry, wells, wetlands, stream flows, and so on. The water table may rise during periods of heavy rain or melting snow, or fall during drier periods, or as a result of extraction.

In some parts of the world, water shortages can be experienced when groundwater supplies are used faster than they are replenished, while in other regions, groundwater can cause flooding or can become polluted by human activities such as industry and agriculture.

Nearly 30% of global freshwater originates from groundwater, and almost all the water used for agriculture, industry and drinking will have been groundwater at some point in its cycle.

Some geological formations are impermeable to groundwater whilst others are permeable. Permeable formations – known as aquifers – have fine holes or networks of fine cracks that allow water to flow through them. The size of the spaces in the soil or rock, as well as how well they are connected, determines the speed of groundwater flow.

In the UK, hydrogeologists are work to ensure groundwater is maintained in sufficient supply with a quality that is protected. In developing countries, hydrogeologists may work on rural water supply projects to help provide safe and accessible water.

NB Groundwater-dependent terrestrial ecosystems are wetlands that are directly dependent on water from a groundwater body to maintain their form and function.

Groundwater source protection zones are areas defined by the Environment Agency which show the risk from contamination/pollution to groundwater that is extracted for drinking water.