|artesian well (är-tē'zhən) Pronunciation Key
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A deep well that passes through impermeable rock or sediment and reaches water that is held under pressure in a confined aquifer. In aquifers of this type, the water in the lower regions is trapped between two layers of impermeable rock and cannot rise to the level of the water table in the upper, unconfined regions. When a well penetrates the confined region, the pressure forces the water to rise within the well until it reaches the elevation of the water table in the unconfined region (a level known as the potentiometric surface). ◇ In a flowing artesian well the water is under enough pressure to rise all the way to the surface without being pumped and must be capped to control the flow.