All the water that flows out of every spring once fell as rain. The rainwater soaks into the soil and enters into rocks through cracks. Of course, much of the rainwater remains near the surface and evaporates into the air, or plants absorb it through their roots.
The rest of the rainwater is drawn downward by gravity, and it goes as far down as the openings in the rocks will allow. Below the surface of the land, but at a different depth in each place, there is a zone where all the openings in the rocks are completely filled with water.
This is called the groundwater zone. The upper surface of this water is called the water table. A spring occurs when water finds a natural opening in the ground that is below the water table.
That’s why most springs are in valleys or low places, the groundwater escapes as spring water through the cracks in the rocks along the sides or bottoms of these low places. A spring doesn’t defy gravity, it is always flowing down from some water level above it.
Some springs receive water from deep within the water zone. These usually flow all year and are called permanent springs. Other springs have their openings near the water table. They usually flow only in the rainy season when the water table is at its highest. These are called intermittent springs.
Since all spring water passes through rocks during its underground travels, all spring water carries some mineral matter, such as sulfur or lime. Springs that have water containing an unusual amount of mineral matter are called mineral springs.
In some places, especially in areas where there have been volcanoes, the water in springs has been in contact with hot, underground rocks. This type of spring is called a thermal or hot spring.
An artesian well is quite different from a spring. In an artesian well, the rainwater sinks down into the ground until it reaches a layer of porous rock or sand that is buried between two layers of solid rock.
Pressure is built up around this water, and when a hole is bored down to reach it, the water escapes with a gush. The well must be driven at a point lower than that at which the water enters the ground.
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