Spring

Spring, in geology, naturally occurring flow of water from the ground. Some are outflows from underground streams, but most often a spring occurs when an aquifer (a layer of water-bearing porous rock or sediment) intersects with the earth's surface. Such an aquifer may travel for hundreds of kilometers underground before emerging to the surface. Spring water is generally fairly clean, since it has been filtered through permeable rocks, but all spring water contains some dissolved minerals.