In this case, the rocks surrounding the aquifer confines the pressure in the porous rock and its water. This is an example of a confined aquifer. There might be a confining layer of less porous rock both above and below the porous layer. Sometimes the porous rock layers become tilted in the earth.
Learn the basics about water using our Water Primers! A Primer on Water (PDF)A Primer on Ground Water (PDF)Ground water and the Rural Homeowner You can see this in the two drawings at the bottom of the diagram, which show a close-up of how water is stored in between underground rock particles. The "unsaturated zone" above the water table (the gray area) still contains water (after all, plants' roots live in this area), but it is not totally saturated with water. In the diagram below, you can see how the ground below the water table (the blue area) is saturated with water. In fact, pumping your well too much can even cause your neighbor's well to run dry if you both are pumping from the same aquifer. Pumping too much water too fast draws down the water in the aquifer and eventually causes a well to yield less and less water and even run dry. The rate of recharge is not the same for all aquifers, though, and that must be considered when pumping water from a well. Precipitation eventually adds water ( recharge) into the porous rock of the aquifer. Wells can be drilled into the aquifers and water can be pumped out. When a water-bearing rock readily transmits water to wells and springs, it is called an aquifer. These rocks have different porosity and permeability characteristics, which means that water does not move around the same way in all rocks below ground.
At the beach, the level of the water table is always at the same level as the ocean, which is just below the surface of the beach.Īs you may have read, most of the void spaces in the rocks below the water table are filled with water. In our sand hole example, you have essentially dug a "well" that exposes the water table, with an aquifer beneath it. The saturated area beneath the water table is called an aquifer, and aquifers are huge storehouses of water. The upper surface of this water-filled area, or "zone of saturation", is called the water table. Have you ever dug a hole at the beach and watched as it partially filled with water from the underlying sand? This is a great way to illustrate the concept of how the ground, if it is permeable enough, can hold water but still stay solid. Groundwater is one of our most valuable resources-even though you probably never see it or even realize it is there. The upper surface of this zone of saturation is called the water table. A hole dug at the beach illustrates the concept of how the ground, if it is permeable enough, can hold water.
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