Water is fundamental to every living being on Earth. Up to 70% of the human body is made up of water, and it is the medium in which the chemical reactions necessary to sustain life take place.

The water cycle, also referred to as the hydrological cycle, is made up of different processes which move water around the Earth. There is a finite amount of water found in different hydrological stores, located above and below the Earth’s surface. Processes such as precipitation, groundwater flow, infiltration, and condensation transport water from one store to another.

A 3D view of the water cycle. Towards the back of the image, precipitation is shown as rain over a mountain range, rain over a forest indicates interception. Arrows from the land and ocean to the atmosphere represent evaporation, and arrows from the tree canopy to the atmosphere represent transpiration. Infiltration is shown as water entering the soil, which then becomes groundwater flow deep underground. Surface runoff is indicated as water running downhill over the land surface, and condensation is represented as clouds.
Figure 1: A labeled overview of the water cycle