What is true about the pressure in an unconfined aquifer?

In an unconfined aquifer, the water table is open to the atmosphere, which means that the pressure within the aquifer is equal to the atmospheric pressure at the water table level. When water is extracted, the level of the water table may drop, but the pressure remains at atmospheric levels because there is no confining layer above to create additional pressure. This characteristic distinguishes unconfined aquifers from confined aquifers, where the water is trapped under a layer of impermeable rock or sediment and can be under considerable pressure. Thus, atmospheric pressure is the defining feature of the pressure system within an unconfined aquifer.