The water cycle

The oceans with their vast water masses cover most of our planet. It makes them one of the most important water reservoirs on Earth. This water moves in a continuous cycle, driven and maintained by the sun and gravity. But how exactly does this cycle work?

The sun‘s radiation heats the water of the oceans, and water molecules rise into the atmosphere in large quantities as water vapour. On dry land,  this evaporation takes place to a lesser extent, which is why the water bound in the Earth‘s atmosphere is not evenly distributed across the globe.

Water can remain in the atmosphere from a few hours to several weeks; on average, it lasts about nine to ten days. Due to the temperature differences between the Earth‘s atmosphere and surface, the water vapour cools down again and condenses, and clouds form. Winds move these humid air masses towards land. As soon as warm and humid layers of air meet cold air, the warm air moves upwards above the cold air. Rising air cools down and loses the ability to store water. The supersaturated air finally releases the accumulated water and precipitation in the form of rain, hail or snow is created. The state in which the precipitation falls depends on the ambient temperatures.

If the precipitation falls directly into bodies of water, the circle closes, and it starts all over again. Above land, however, water takes a different path. There it seeps into groundwater and via the groundwater flow, springs and rivers it returns to the oceans. Through rivers, melt-water from glaciers and snow also reach the oceans. However, precipitation that falls over a city ends up in the sewerage system and cannot contribute to the formation of new groundwater.

This cycle is the basis  to obtain drinking water from ground, surface and spring water. After use, wastewater reaches sewage treatment plants and after being cleaned flows back into the rivers.