Artesian wells contain water under pressure due to the geological conditions surrounding the aquifer from which the water is drawn. Here's how it works:
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Aquifer Formation: An artesian aquifer is typically formed when water is trapped between two layers of impermeable rock or clay, which creates a confined space. The water is usually collected from rain or other sources that have seeped into the ground far away from the actual well location, potentially from higher elevations.
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Hydrostatic Pressure: Due to the weight of the water above it and the surrounding rock layers, the water in the confined aquifer is placed under hydrostatic pressure. This pressure can build up over time, especially when the area receives a good amount of precipitation or when water is seeping in from higher ground.
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Well Drilling: When a well is drilled into this confined aquifer, the pressure causes water to rise up through the well, sometimes even reaching the surface without any pumping. This is because the pressure in the aquifer is greater than the atmospheric pressure at the wellhead.
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Pressure Dynamics: If the pressure is sufficient, the water in an artesian well can flow freely to the surface, creating what is known as a flowing artesian well. However, if the pressure is lower or if some of the pressure has been released due to extraction, the water may rise only to a certain level, known as the piezometric surface, rather than flowing out of the well.
Overall, the combination of geological formations, the confinement of water filled with pressure, and the process of drilling into the aquifer results in the presence of water under pressure in artesian wells.