In the future, water may be our most valuable commodity. Understanding the water cycle – the continuous movement of water through the Earth's upper crust, surface and atmosphere – is crucial.

This resource provides explanations of the key concepts encountered when exploring the water cycle.

Water cycle

The water cycle involves water moving through the different Earth subsystems so that it is being recycled.

The water cycle is dynamic and complex

Time and space are important variables that influence the water cycle. Water is stored in the atmosphere, oceans, groundwater, ice and snow, and freshwater.

Earth system

The Earth system is made up of 4 subsystems – atmosphere, biosphere, geosphere and hydrosphere.

Earth subsystems

There are 4 subsystems in the Earth system. The atmosphere is the layer of gases that surround the Earth. The biosphere consists of all the living organisms on Earth. The geosphere is the physical Earth, the rock magma and soil. The hydrosphere is all the water held on the Earth.

Moving between subsystems

Various physical and chemical processes cause materials and heat energy to move within and between Earth’s subsystems, often in cyclic patterns, for example, processes like evaporation, transpiration, sublimation, precipitation, infiltration, run-off, groundwater discharge and stream flow circulate water throughout the Earth system, forming the water cycle.

The total amount of water on Earth is finite (almost)

The original source of water is derived from cooling magma, and water is distributed globally in saline and in freshwater – icecaps and glaciers, groundwater (springs and aquifers), lakes, swamps, rivers. Changing temperature has an impact on global water distribution (past and future scenarios).

The water cycle influences weather patterns and climate

Ocean currents (cold and warm) transport heat and transfer water to the atmosphere via evaporation. Weather patterns can be linked to ocean currents and air temperature (i.e. precipitation/droughts or winds and hurricanes).

Human activity can impact on the water cycle

  • Use of water for hydroelectric power and irrigation removes water from the natural cycle.
  • Deforestation.
  • Production of greenhouse gases (farming, industry, transport, etc.) have an impact on global warming.
    Published 28 May 2009