What characterizes a confined aquifer?

A confined aquifer is characterized by being bounded by confining units, which are layers of impermeable rock or sediment located both above and below the aquifer. This structure creates pressure within the aquifer, as the water is trapped between layers that do not allow it to flow freely to the surface. As a result, water in a confined aquifer can often rise to the surface when tapped by a well, a phenomenon known as artesian flow.

In contrast, an unconfined aquifer is open to the atmosphere and typically recharges easily from precipitation and surface water. The characteristics of water composition and recharge dynamics are not confined solely to rainwater or limited by surrounding aquifers in the way described, making the other options less accurate in defining a confined aquifer.