Groundwater is the water that lies beneath the water-table.
Think of groundwater as being like an underground reservoir of water, sitting within a basin of impermeable rock. Ground water is typically pumped out of the soil for human used, particularly in cities such as London where it is pumped out to about 65M below ground, below the underground system.
A building in contact with groundwater is at risk of its walls drawing up moisture through absorption, this is known as rising damp.
Water suspended in soil above the water table is not groundwater. Rain may temporarily flood surface soil, in time excess moisture will percolated down to the water table to become groundwater.
Tips for identifying groundwater
- Drill below the level of your house and test for free water.
- Test for nitrates associated with groundwater. If there are no nitrate salts then your dampness is not caused by groundwater, or rising damp. Mains water and salts that originate from water in contact with manure or chimney breasts can also contact nitrate salts.
- Look up local water table, flood risk, height of property above large lake or sea level, for at underlying rock.