At a spring, water comes up from the ground to the surface. This water is called groundwater. Several springs usually join to form a stream and later a river that flows into the sea.
Most of the time it is rainwater that has seeped into the ground. It seeks its way through the earth until it comes out of a layer of rock or clay. The water can't get through there and flows along this layer. At some point, it usually finds its way to the surface.
As water flows through the ground, it is purified as if by a filter. Springs that come from the depths therefore usually carry very clean water that can be used directly as drinking water. However, if the rainwater seeps into a pasture or a field with a lot of fertiliser and then comes right back to the surface, the water can be harmful to humans.
Some springs give very warm water, these are the thermal springs. The water is warm because it comes from deep in the earth, where it is hot. Or it has been heated by a volcano. Other springs have substances in them, such as minerals. If such substances are good for your health, it is called a healing spring.
What else can the word "spring" mean?
The word "spring" is not only used for water that comes from the earth. By "source" one often simply means the origin of a news item. When you read something in the newspaper, you sometimes wonder where it comes from. So you wonder how the writer knows. Maybe he saw it himself, that would be a safe source. But maybe he only heard it or read it somewhere himself, that would be an uncertain source.
There are different kinds of such sources. A person can be a source if he tells what he has seen or experienced himself. An old letter can be a source for historical research, but also an old gravestone or an inscription on a house. Old paintings are also sometimes good sources. However, one has to ask oneself whether the writer or the painter has not perhaps exaggerated.