The water table, or phreatic surface, is the level at which the groun water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the ground water in a given vicinity. As water infiltrates through pore spaces in the soil, it first passes through the zone of aeration, where the soil is unsaturated. At increasing depths water fills in more spaces, until the zone of saturation is reached. This relatively horizontal plane atop this zone constitutes the 'water table'.