Posted: 23 January 2001

The water that accumulates in the pore spaces and cracks in rocks beneath the earth's surface. It originates as precipitation and percolates down into sub-surface aquifers. The upper limit of groundwater saturation is the water table. Groundwater moves under the influence of gravity, although usually only slowly, and may return to the surface naturally - for example, through springs. Increasingly, it is pumped from wells and boreholes for human use. The rate of withdrawal commonly exceeds the rate the rate of recharge, and in many areas the groundwater supply is simply declining.