An artesian well is a pumpless water source that uses pipes to allow underground water that is under pressure to rise to the surface. This type of 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. In addition, the water has been naturally filtered because it passes through porous rock as it seeps into the Earth to reach the aquifer, which is the underground water source. For centuries, people have drilled artesian wells to drink filtered water that doesn't need to be manually or mechanically hauled up from the depths.
An aquifer provides the water source for an artesian well. This is the layer of permeable rock, such as 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, such as clay soil or shale rock. This keeps the water pressure high, so that at a point below the entryway of the flow, there is enough pressure to bring the water up when the pressure is released. Natural springs form in the same way when a gap in the impermeable rock — perhaps triggered by an earthquake — allows the water to rise to the surface. Sometimes, if the pressure is especially strong in the aquifer, the water might thrust up like a fountain and form a geyser.
Artesian wells are found all over the world. Entire cities have relied on giant underground aquifers to provide fresh, cold water when there are no above-ground rivers. Where modern plumbing is scarce or nonexistent, people often must rely on an artesian well for clean water. The Great Artesian Basin, which provides fresh water to inland Australia, is the largest such basin in the world. Thousands of artesian wells have tapped into this aquifer.
The first known artesian well was drilled in 1126 by a group of monks who used a rod with a sharp end, called a bore, to penetrate a layer of impermeable rock to reach an aquifer. Their percussive drilling — just hammering on the end of the bore — broke through the rock with sheer human force. The water that rose to the surface had seeped through the pores of the rock, so that many contaminants have been filtered out, and it proved to be safer to drink than standing water from the surface or river water.