An artesian well allows water to rise to the surface that has traveled through porous rock from a higher elevation. This pumpless well seems to defy gravity because the pressure that builds up between layers of rock gets relieved when the water finds a path to the open air. For nearly a thousand years, people have drilled wells to drink such cold, filtered water that doesn't need to be hauled up from the depths.

An aquifer provides the water source for an artesian well. An aquifer is the layer of permeable rock, like limestone or sandstone, that absorbs water from an inlet path at high elevation such as the top of a mountain. The water source might be fed by snowmelt or precipitation. Porous stone is sandwiched between a top and bottom layer of an impermeable substance like clay soil or shale rock. This keeps the water pressure high, so that when you get to a point below the entryway of the flow, there is enough pressure to bring the water up. Natural springs form in the same way when a gap in the impermeable rock, maybe triggered by an earthquake, allows the water to rise to the surface.

Entire cities have relied on giant underground aquifers to provide fresh, cold water when there are no above-ground rivers. In 1126, monks used a rod with a sharp end, called a bore, to penetrate a layer of impermeable rock. Their percussive drilling, just hammering on the end of the bore, broke through with sheer human force. The water that rose had percolated through the pores of the rock, so that many contaminants have been filtered out, and it proved safer to drink than standing or river water.

Nowadays, if a town or residency needs water closer to the top of a mountain, they might lie above the line where there is enough pressure to push the water all the way to the surface. In this case, the aquifer can be accessed by drilling a relatively shallow well and then pumping the water up to ground level. Our well-drilling has progressed from hammers and bores, to machinery that twists a giant drill into the ground. Sometimes, if the pressure is especially strong, because the well is lower in elevation, the water might thrust up like a fountain, and form a geyser.