residence time
Water can remain in a particular location for a long time. This is known as a reservoir . Reservoirs for water include oceans, glaciers, ponds, or even the atmosphere. A water molecule may pass through a reservoir very quickly or may remain for much longer. The amount of time a molecule stays in a reservoir is known as its residence time . The residence time of water in the ocean is 3,200 years. Of course, not every molecule stays that long. That number is an average for all molecules.