Groundwater & springs

When it rains, a large part of the water seems to disappear into the ground. But it is not gone, it slowly seeps downward and gathers deep in the earth. This hidden water is called groundwater. In Germany about 70 percent of drinking water comes from groundwater and spring water, so what runs out of your tap has usually travelled through the ground first.

Seeping into the ground

Whether water seeps in depends on the ground below. Sand and gravel have many small gaps through which water runs easily. Such layers are called permeable. Solid clay, on the other hand, is dense and holds the water back almost completely. The seeping water gradually fills the pores between the grains, much like water soaking into a sponge.

Water bearing layers

The seeping water sinks until it meets an impermeable layer such as clay. There it backs up and fills the permeable layer above it like an underground sponge. Such a water filled layer is called an aquifer. The upper edge of this body of water, up to which every pore is filled, is called the water table. After wet weeks it rises, after a dry summer it sinks again.

Springs and drinking water

Where the water table reaches the surface, water comes out on its own. That is a spring, often the start of a stream. To reach the deeper groundwater, people dig or drill wells. Because groundwater is filtered by the soil layers, it is usually clean and provides our drinking water in many places. It is not clean all on its own, though: dissolved substances such as nitrate from fertiliser seep down with the water, which is why drinking water is tested in a lab on a regular basis.