A water molecule finds its way from the ocean when it is heated by the heat from the sun. The water molecule, which was once in the form of a liquid, changes to a vapor state. The molecule is moved to the upper sides of the atmosphere by movements of the air currents, where it becomes part of the clouds. The clouds are moved around the globe, and by the act of the different clouds colliding with each other, they grow, and with time, they fall out of the atmosphere as precipitation of different forms. Most of the precipitation falls back directly to the oceans due to the fact that most part of the planet Earth is covered by the ocean.
The water molecule may fall as precipitation on the earth’s surface, where it will be part of the water that flows as surface runoff to the rivers, and the river will direct it back to the ocean. The water molecule can alternatively percolate underground and come out as a spring. Most springs act as sources of rivers, and therefore, the water molecule may continue its journey through the river to the ocean. When the precipitation occurs as snow melts, there is an accumulation of glaciers and ice caps, and this can retain a water molecule for thousands of years. Through the melting of the snow, water can find its way to the river, and the river will drain the water molecules back into the ocean.
A water molecule can, on the other hand, go back to the atmosphere before returning to the ocean. This is, for example, when there is evaporation occurring on the earth’s surface, in rivers, and in lakes. The water molecule will, however, find its way back to the ocean by following one of the channels that leads back to the ocean that are described above. The water molecules can also fall on the earth’s surface and percolate into the deep earth aquifers. The aquifers may have an outlet that drains directly to the ocean, and thus, the water molecule will have its way back to the ocean.