Groundwater is a hidden, but important resource. We can practicably define groundwater as water be· neath the ground surface that can be extracted by wells. Other water in the ground that is not considered to be available for man's direct use is commonly called "subsurface water." Subsurface water includes moisture within the root zone.
Peralta, Richard C., "Assuring a Long Term Groundwater Supply: Issues, Goals and Tools" (1989). All Archived Publications. Paper 420.