The water table

The water table is a fundamental concept in hydrogeology, yet it is frequently incorrectly defined. For example, both the NGWA (2003) and AGI (Neuendorf et al. 2005) glossaries define the water table as the atmospheric pressure surface that is coincident with the top of the zone of saturation. This definition is also found occasionally in groundwater textbooks as well as in primers, where it is simply defined as the top of the zone of saturation. This incorrect definition of the water table perpetuates an important conceptual misunderstanding in hydrogeology that the top of the zone of saturation is uniquely related to the water table. This commentary reviews the correct definition of the water table and addresses evidence for unsaturation beneath the water table.