What defines the water table in a groundwater system?

The water table is defined as the upper limit of the zone of saturation within a groundwater system. This is the level below which the soil and rock are fully saturated with water and above which the pores in the soil or rock contain both air and water. When precipitation occurs, water infiltrates the ground until it reaches this point, at which the spaces between soil particles are fully filled with water.

As for the other choices, the boundary between unsaturated and saturated zones, while related, does not fully capture the essence of the water table itself, which specifically refers to the uppermost surface of the saturated zone. The depth where groundwater can be collected is influenced but not solely defined by the water table, as it may vary based on well construction and local hydrogeological conditions. Lastly, the point at which soil remains constantly moist may occur within the saturated zone but does not specifically define the water table, as the water table can fluctuate with changes in precipitation and extraction.