The water table: Its conceptual basis, its measurement and its usefulness as a hydrological variable

The water table, as used routinely by hydrologists in various disciplines, is seemingly a simple concept: it marks the top of the saturated zone in porous media. But closer inspection reveals that much of the theory and practice concerning the water table are less straightforward than is often assumed. We review departures from the classical definition of the water table and consider the following phenomena: perched and inverted water tables, gas bubbles within the “saturated” zone below the water table, and water tables in dual (and multiple) porosity media. We discuss some of the different methods used for measuring the position of the water table, their relative practicalities, and how to avoid measurement errors, such as those associated with hydrological instrument response times. We question whether the water table remains a useful concept, and conclude that it does, citing the examples of groundwater resource management and the water table's use as an indicator of soil aeration. In the concluding discussion, we identify the precautions that can be taken to ensure water tables are appropriately measured and interpreted.