Groundwater

Rainfall which infiltrates the soil and penetrates to the underlying strata is called groundwater. The quantity of water which can be accommodated under the surface depends on the porosity of the sub-surface strata. The water bearing strata, called aquifers, may consist of unconsolidated materials like sands, gravels and glacial drift or consolidated material like sandstones and limestones. Limestone is relatively impervious but is soluble in water and so frequently has wide joints and solution passages which make the rock, en masse, similar to a porous rock in its capacity to hold water and act as an aquifer.