Underground water flows to emerge into a stream.

Groundwater moves underground

Of course, the source of all water is precipitation, the downward arrows coming down from the top in the diagram. Some of the water hitting the landscape runs downhill and into the stream (purple arrow)—this is runoff. The tan area is the unsaturated zone, which is the top layer of the ground which gets saturated during a heavy rainfall, stays wet but not saturated, after a rainfall, and can become quite dry during times when no precipitation falls. This zone is the area that plants put down roots in, and thus draw water from. The green arrow shows that water moves up from the unsaturated zone into the plants and then out of the plants as evapotranspiration.