The groundwater gradient and flow directions can be determined from the groundwater contour lines. The amount of subterranean groundwater can then be estimated from the groundwater gradient and flow direction. Particularly when monitoring groundwater contamination, it must be determined where a pollutant originates and what its fate is. Knowledge of the groundwater surface is also important for the delineation of catchment areas, for the establishment of drinking water protection areas, for the assessment of water exchange with surface waters, and for the assessment of size and extent of (deeper) aquifers and permeability.