What is an artesian well?

When the pressure in an aquifer causes the water in a well to rise above the top of the aquifer, it's called an artesian well. In the example showed in Figure 1, the top of the aquifer is just above the top of the screen — with the confining layer above the aquifer — but the piezometric level or water level is much closer to the surface. Aquifers, like all geologic formations, are rarely flat. And in this example, we see the geologic formations rising on the right side of the diagram. The pressure causing the water in the well to be so high comes from water entering the aquifer in the recharge area on the right.

To put this another way, let's say you are holding a short hose full of water with both ends pointing up, and one end higher than the other. If you pour water in the high end, the water will flow out of the other lower end because the new water pushes it out. That's what's happening in the aquifer in the figure. The recharge area is in effect the high end of the hose, and water infiltrating into the aquifer there creates the pressure that causes water in the well to rise above the top of the aquifer formation. If the land surface conditions are just right, a well on a lower part of the landscape could actually be flowing because the top of the well is at a lower elevation than the recharge area supplying water to the aquifer. This is a flowing artesian well.

Some states have rules about flowing wells because they discharge so much groundwater. There are pitless adapter designs meant to prevent these wells from flowing. In western states like South Dakota, well regulations require owners of flowing wells to limit flow to actual use and/or to the limit of their water rights permit.

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