What type of well requires a confined aquifer under a sloping aquitard?

An artesian well relies on the characteristics of a confined aquifer, which exists when water is trapped between layers of impermeable material, such as an aquitard. The pressure within the confined aquifer can be sufficient to force water to rise naturally to the surface when a well is drilled, creating a discharge without the need for pumping. The presence of a sloping aquitard above the aquifer allows for pressure to build up, enabling this natural flow. This phenomenon is what differentiates artesian wells from other types, as they are specifically associated with this unique geologic setup where groundwater is under pressure.

In contrast, springs occur where groundwater naturally flows to the surface without being confined, unconfined wells draw water from aquifers without pressure support, and deep wells refer more generally to wells that extend deep into the ground, not necessarily tied to the confined or unconfined nature of the aquifer. The key feature of artesian wells is the specific conditions of confinement and pressure that allow water to rise freely, which leads to their unique functioning.