Some basic concepts of Aquifers An aquifer is a layer of relatively porous substrate that contains and transmits groundwater.When water can flow directly between the surface and the saturated zone of an aquifer,the aquifer is unconfined.The deeper parts of unconfined aquifers are usually more saturated with groundwater since gravity causes water to flow downward.Some basic concepts of Aquifers An aquifer is a layer of relatively porous substrate that contains and transmits groundwater. When water can flow directly between the surface and the saturated zone of an aquifer, the aquifer is unconfined. The deeper parts of unconfined aquifers are usually more saturated with groundwater since gravity causes water to flow downward