A water molecule consists of two hydrogen atoms and one oxygen atom
The three common states of matter
Phase diagram of water (simplified)
Time-mean precipitation and evaporation as a function of latitude as simulated by an aqua-planet version of an atmospheric GCM (GFDL's AM2.1) with a homogeneous “slab-ocean” lower boundary (saturated surface with small heat capacity), forced by annual mean insolation.
Tetrahedral structure of water
Global map of annual mean evaporation minus precipitation by latitude-longitude
Model of hydrogen bonds (1) between molecules of water
Relationship between impervious surfaces and surface runoff
Water cycle
Diagram of the water cycle
Overview of photosynthesis (green) and respiration (red)
Natural water cycle
Water fountain
An environmental science program – a student from Iowa State University sampling water
Total water withdrawals for agricultural, industrial and municipal purposes per capita, measured in cubic metres (m³) per year in 2010
A young girl drinking bottled water
Water availability: the fraction of the population using improved water sources by country
Roadside fresh water outlet from glacier, Nubra
Hazard symbol for non-potable water
Water is used for fighting wildfires.
San Andrés island, Colombia
Water can be used to cook foods such as noodles
Sterile water for injection
Band 5 ALMA receiver is an instrument specifically designed to detect water in the universe.
South polar ice cap of Mars during Martian south summer 2000
An estimate of the proportion of people in developing countries with access to potable water 1970–2000
People come to Inda Abba Hadera spring (Inda Sillasie, Ethiopia) to wash in holy water
Icosahedron as a part of Spinoza monument in Amsterdam.
Water requirement per tonne of food product
Irrigation of field crops
Specific heat capacity of water

The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth.

- Water cycle

Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.

- Water
A water molecule consists of two hydrogen atoms and one oxygen atom

8 related topics

Alpha

Visualisation of the distribution (by volume) of water on Earth. Each tiny cube (such as the one representing biological water) corresponds to approximately 1400 cubic km of water, with a mass of approximately 1.4 trillion tonnes (235000 times that of the Great Pyramid of Giza or 8 times that of Lake Kariba, arguably the heaviest man-made object). The entire block comprises 1 million tiny cubes.

Fresh water

Visualisation of the distribution (by volume) of water on Earth. Each tiny cube (such as the one representing biological water) corresponds to approximately 1400 cubic km of water, with a mass of approximately 1.4 trillion tonnes (235000 times that of the Great Pyramid of Giza or 8 times that of Lake Kariba, arguably the heaviest man-made object). The entire block comprises 1 million tiny cubes.
A graphical distribution of the locations of water on Earth. Only 3% of the Earth's water is fresh water. Most of it is in icecaps and glaciers (69%) and groundwater (30%), while all lakes, rivers and swamps combined only account for a small fraction (0.3%) of the Earth's total freshwater reserves.

Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids.

Fresh water is replenished through the process of the water cycle, in which water from seas, lakes, forests, land, rivers and reservoirs evaporates, forms clouds, and returns inland as precipitation.

An illustration showing groundwater in aquifers (in blue) (1, 5 and 6) below the water table (4), and three different wells (7, 8 and 9) dug to reach it.

Groundwater

An illustration showing groundwater in aquifers (in blue) (1, 5 and 6) below the water table (4), and three different wells (7, 8 and 9) dug to reach it.
Dzherelo, a common source of drinking water in a Ukrainian village
The entire surface water flow of the Alapaha River near Jennings, Florida, going into a sinkhole leading to the Floridan Aquifer groundwater
Groundwater may be extracted through a water well
Diagram of a water balance of the aquifer
Iron (III) oxide staining (after water capillary rise in a wall) caused by oxidation of dissolved iron (II) and its subsequent precipitation, from an unconfined aquifer in karst topography. Perth, Western Australia.
Groundwater withdrawal rates from the Ogallala Aquifer in the Central United States
Center-pivot irrigated fields in Kansas covering hundreds of square miles watered by the Ogallala Aquifer

Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations.

Groundwater can be a long-term 'reservoir' of the natural water cycle (with residence times from days to millennia), as opposed to short-term water reservoirs like the atmosphere and fresh surface water (which have residence times from minutes to years).

Runoff flowing into a stormwater drain

Surface runoff

Runoff flowing into a stormwater drain
Surface runoff from a hillside after soil is saturated
Precipitation washing contaminates into local streams
Urban surface water runoff
Willow hedge strengthened with fascines for the limitation of runoff, north of France.
Soil erosion by water on intensively-tilled farmland.
Farmland runoff
Runoff holding ponds (Uplands neighborhood of North Bend, Washington)

Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil.

Surface runoff is a major component of the water cycle.

Ice

The three-dimensional crystal structure of H2O ice Ih (c) is composed of bases of H2O ice molecules (b) located on lattice points within the two-dimensional hexagonal space lattice (a).
Pressure dependence of ice melting
Log-lin pressure-temperature phase diagram of water. The Roman numerals correspond to some ice phases listed below.
An alternative formulation of the phase diagram for certain ices and other phases of water
Frozen waterfall in southeast New York
Feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (−22 °F).
Ice on deciduous tree after freezing rain
A small frozen rivulet
Ice formation on exterior of vehicle windshield
An accumulation of ice pellets
A large hailstone, about 6 cm in diameter
Snowflakes by Wilson Bentley, 1902.
Harvesting ice on Lake St. Clair in Michigan, c. 1905
Layout of a late 19th-Century ice factory
Loss of control on ice by an articulated bus
Channel through ice for ship traffic on Lake Huron with ice breakers in background
Rime ice on the leading edge of an aircraft wing, partially released by the black pneumatic boot.
Skating fun by 17th century Dutch painter Hendrick Avercamp
Ice pier during 1983 cargo operations. McMurdo Station, Antarctica

Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or 32 degrees Fahrenheit.

It is abundant on Earth's surface – particularly in the polar regions and above the snow line – and, as a common form of precipitation and deposition, plays a key role in Earth's water cycle and climate.

Water cycle of the Earth's surface, showing the individual components of transpiration and evaporation that make up evapotranspiration. Other closely related processes shown are runoff and groundwater recharge.

Evapotranspiration

Term used to refer to the combined processes by which water moves from the earth’s surface into the atmosphere.

Term used to refer to the combined processes by which water moves from the earth’s surface into the atmosphere.

Water cycle of the Earth's surface, showing the individual components of transpiration and evaporation that make up evapotranspiration. Other closely related processes shown are runoff and groundwater recharge.
Monthly estimated potential evapotranspiration and measured pan evaporation for two locations in Hawaii, Hilo and Pahala.
Classification of RS-based ET models based on sensible heat flux estimation approaches

Evapotranspiration is an important part of the local water cycle and climate, as well as measurement of it plays a key role in agricultural irrigation and water resource management.

Potential evapotranspiration (PET) is the amount of water that would be evaporated and transpired by a specific crop, soil or ecosystem if there were sufficient water available.

Mean precipitation based on global high resolution climate data (CHELSA)

Precipitation

Any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds.

Any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds.

Mean precipitation based on global high resolution climate data (CHELSA)
Countries by average annual precipitation
A thunderstorm with heavy precipitation
Late-summer rainstorm in Denmark
Lenticular cloud forming due to mountains over Wyoming
Condensation and coalescence are important parts of the water cycle.
Puddle in the rain
An accumulation of ice pellets
A large hailstone, about 6 cm in diameter
Snowflake viewed in an optical microscope
Convective precipitation
Orographic precipitation
Lake-effect snow bands near the Korean Peninsula in early December 2008
Rainfall distribution by month in Cairns showing the extent of the wet season at that location
Standard rain gauge
Updated Köppen-Geiger climate map
Rainfall estimates for southern Japan and the surrounding region from July 20 to 27, 2009.
Extreme precipitation events have become more common in the U.S. over recent decades.
Image of Atlanta, Georgia, showing temperature distribution, with hot areas appearing white
Example of a five-day rainfall forecast from the Hydrometeorological Prediction Center

Precipitation is a major component of the water cycle, and is responsible for depositing fresh water on the planet.

Mineralogical evidence from zircons shows that liquid water and atmosphere were believed to have existed 4.404 billion years ago, shortly after the Earth was formed.

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Cloud

Aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space.

Aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space.

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Stratocumuliform cloudscape
Tropospheric cloud classification by altitude of occurrence: Multi-level and vertical genus-types not limited to a single altitude level include nimbostratus, cumulonimbus, and some of the larger cumulus species.
Cumulus humilis clouds in May
Windy evening twilight enhanced by the Sun's angle, can visually mimic a tornado resulting from orographic lift
Nimbostratus cloud producing precipitation
Cirrus fibratus clouds in March
Stratocumulus over Orange County.
Stratocumulus cloud
Cumulus humilis clouds
Cumulonimbus cloud over the Gulf of Mexico in Galveston, Texas
High cirrus upper-left merging into cirrostratus and some cirrocumulus upper right
A large field of cirrocumulus
Sunrise scene giving a shine to an altocumulus stratiformis perlucidus cloud (see also 'species and varieties')
Altostratus translucidus near top of photo merging into altostratus opacus near bottom
Cumulus humilis clouds over Jakarta, Indonesia
Stratocumulus stratiformis perlucidus over Galapagos, Tortuga Bay (see also 'species and varieties')
Stratus nebulosus translucidus
Deep multi-level nimbostratus cloud covering the sky with a scattered layer of low stratus fractus pannus (see also 'species' and 'supplementary features' sections)
Cumulus humilis and cumulus mediocris with stratocumulus stratiformis perlucidus in the foreground (see also 'species and varieties')
Towering vertical cumulus congestus embedded within a layer of cumulus mediocris: Higher layer of stratocumulus stratiformis perlucidus.
Progressive evolution of a single cell thunderstorm
Isolated cumulonimbus cloud over the Mojave Desert, releasing a heavy shower
Altocumulus lenticularis forming over mountains in Wyoming with lower layer of cumulus mediocris and higher layer of cirrus spissatus
Example of a castellanus cloud formation
Cumulus mediocris cloud, about to turn into a cumulus congestus
A layer of stratocumulus stratiformis perlucidus hiding the setting sun with a background layer of stratocumulus cumulogenitus resembling distant mountains.
Cirrus fibratus radiatus over ESO's La Silla Observatory
Altocumulus stratiformis duplicatus at sunrise in the California Mojave Desert, USA (higher layer orange to white; lower layer grey)
Cumulus partly spreading into stratocumulus cumulogenitus over the port of Piraeus in Greece
Cumulonimbus mother cloud dissipating into stratocumulus cumulonimbogenitus at dusk
Cirrus fibratus intortus formed into a Kármán vortex street at evening twilight
Global cloud cover, averaged over the month of October 2009. NASA composite satellite image.
Lenticular nacreous clouds over Antarctica
Noctilucent cloud over Estonia
Joshua Passing the River Jordan with the Ark of the Covenant (1800) by Benjamin West, showing Yahweh leading the Israelites through the desert in the form of a pillar of cloud, as described in
Stratocumulus stratiformis and small castellanus made orange by the sun rising
An occurrence of cloud iridescence with altocumulus volutus and cirrocumulus stratiformis
Sunset reflecting shades of pink onto grey stratocumulus stratiformis translucidus (becoming perlucidus in the background)
Stratocumulus stratiformis perlucidus before sunset. Bangalore, India.
Late-summer rainstorm in Denmark. Nearly black color of base indicates main cloud in foreground probably cumulonimbus.
Particles in the atmosphere and the sun's angle enhance colors of stratocumulus cumulogenitus at evening twilight

Water or various other chemicals may compose the droplets and crystals.

Nevertheless, it was the first known work that attempted to treat a broad range of meteorological topics in a systematic way, especially the hydrological cycle.

The Pacific Ocean, part of Earth's hydrosphere

Hydrosphere

The Pacific Ocean, part of Earth's hydrosphere
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The hydrosphere is the combined mass of water found on, under, and above the surface of a planet, minor planet, or natural satellite.

The water cycle refers to the transfer of water from one state or reservoir to another.