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At the groundwater table the water pressure is equal to atmospheric pressure.
Below the groundwater table, the water is under hydrostatic pressure, which is greater than the atmospheric pressure, and it increases with depth just like in a pool.
Above the groundwater table capillary suction prevails and the water pressure is less than atmospheric.
Compared to water in a pool, the groundwater table corresponds to the water surface in the pool.
Unlike the soil, a pool does not have capillaries above the water surface and there is no water hanging above it.
In a soil, the zone above the water table is called unsaturated (or vadose) zone. Depending on the moisture content of the unsaturated zone, there is more or less air in it.
Below the groundwater table no air present, unless entrapped or dissolved in the water.
The level of groundwater table (or groundwater level) can be detected by perforating a hole into the soil until water starts entering it. Then wait until the hole is no longer filling up. The level of the water surface in the hole now equals the level of the groundwater table.
However, if the perforation, by chance, goes through an impermeable (impervious) soil layer (the aquiclude) below which water occurs under artesian pressure, the driller of the hole may be in for a surprise (because the water suddenly rises up in the hole), and anyway he/she has not detected the water table, as there is none. The underlying aquifer is confined (See "Aquifer types").
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