Aquifers can be unconfined or confined by impermeable rock layers called aquicludes. In an unconfined aquifer, water flows freely. The water table tends to approximate the topography of the landscape. In a confined aquifer, water flow is restricted by impermeable layers called aquicludes. Water flowing downhill beneath an aquiclude may be under pressure. This is artesian flow. Drilling into it will create an artesian well, through which water will flow spontaneously.