Water

A water molecule consists of two hydrogen atoms and one oxygen atom
The three common states of matter
Phase diagram of water (simplified)
Tetrahedral structure of water
Model of hydrogen bonds (1) between molecules of water
Water cycle
Overview of photosynthesis (green) and respiration (red)
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

Inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent ).

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

139 related topics

Alpha

Core of CROCUS, a small nuclear reactor used for research at the EPFL in Switzerland

Nuclear reactor

Atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions.

Atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions.

Core of CROCUS, a small nuclear reactor used for research at the EPFL in Switzerland
An example of an induced nuclear fission event. A neutron is absorbed by the nucleus of a uranium-235 atom, which in turn splits into fast-moving lighter elements (fission products) and free neutrons. Though both reactors and nuclear weapons rely on nuclear chain reactions, the rate of reactions in a reactor is much slower than in a bomb.
The Chicago Pile, the first nuclear reactor, built in secrecy at the University of Chicago in 1942 during World War II as part of the US's Manhattan project
Lise Meitner and Otto Hahn in their laboratory
Some of the Chicago Pile Team, including Enrico Fermi and Leó Szilárd
Primary coolant system showing reactor pressure vessel (red), steam generators (purple), pressurizer (blue), and pumps (green) in the three coolant loop Hualong One pressurized water reactor design
NC State's PULSTAR Reactor is a 1 MW pool-type research reactor with 4% enriched, pin-type fuel consisting of UO2 pellets in zircaloy cladding.
Treatment of the interior part of a VVER-1000 reactor frame at Atommash
In thermal nuclear reactors (LWRs in specific), the coolant acts as a moderator that must slow down the neutrons before they can be efficiently absorbed by the fuel.
Diablo Canyon – a PWR
The CANDU Qinshan Nuclear Power Plant
The Magnox Sizewell A nuclear power station
The Torness nuclear power station – an AGR
Scaled-down model of TOPAZ nuclear reactor
The Superphénix, closed in 1998, was one of the few FBRs.
Three of the reactors at Fukushima I overheated, causing the coolant water to dissociate and led to the hydrogen explosions. This along with fuel meltdowns released large amounts of radioactive material into the air.

This molecule is chemically identical to H2O and so is both colorless and odorless, however the additional neutrons in the hydrogen nuclei cause the tritium to undergo beta decay with a half-life of 12.3 years.

Christian Friedrich Schönbein (18 October 1799 – 29 August 1868)

Ozone

Inorganic molecule with the chemical formula .

Inorganic molecule with the chemical formula .

Christian Friedrich Schönbein (18 October 1799 – 29 August 1868)
A prototype ozonometer built by John Smyth in 1865
Resonance Lewis structures of the ozone molecule
General reaction equation of ozonolysis
The distribution of atmospheric ozone in partial pressure as a function of altitude
Concentration of ozone as measured by the Nimbus-7 satellite
Total ozone concentration in June 2000 as measured by the NASA EP-TOMS satellite instrument
Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. Essentially all UVC (100–280 nm) is blocked by dioxygen (at 100–200 nm) or by ozone (at 200–280 nm) in the atmosphere. The shorter portion of this band and even more energetic UV causes the formation of the ozone layer, when single oxygen atoms produced by UV photolysis of dioxygen (below 240 nm) react with more dioxygen. The ozone layer itself then blocks most, but not quite all, sunburn-producing UVB (280–315 nm). The band of UV closest to visible light, UVA (315–400 nm), is hardly affected by ozone, and most of it reaches the ground.
Ozone cracking in natural rubber tubing
Red Alder leaf, showing discolouration caused by ozone pollution
Signboard in Gulfton, Houston indicating an ozone watch
Ozone production demonstration, Fixed Nitrogen Research Laboratory, 1926
A homemade ozone generator. Ozone is produced in the corona discharge
A laboratory method for the preparation of ozone by using Siemen's Ozoniser.

According to experimental evidence from microwave spectroscopy, ozone is a bent molecule, with C2v symmetry (similar to the water molecule).

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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.

Boy drinks from a tap at a NEWAH WASH water project in Puware Shikhar, Udayapur District, Nepal.

Hydrogeology

Area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aquifers).

Area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aquifers).

Boy drinks from a tap at a NEWAH WASH water project in Puware Shikhar, Udayapur District, Nepal.
Checking wells
Boy under a waterfall in Phu Sang National Park, Thailand.
Demänovská Cave of Liberty, "Emerald Lake"
Karst spring (Cuneo, Piemonte, Italy)
Painting by Ivan Aivazovsky (1841)
A piezometer is a device used to measure the hydraulic head of groundwater.
A water drop.
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[Left] High porosity, well sorted [Right] Low porosity, poorly sorted
Illustration of seasonal fluctuations in the water table.
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Henry Darcy, whose work set the foundation of quantitative hydrogeology
Geometry of a partially penetrating well drainage system in an anisotropic layered aquifer
Relative groundwater travel times.
A water well in Kerala, India.

Hydrogeology is an interdisciplinary subject; it can be difficult to account fully for the chemical, physical, biological and even legal interactions between soil, water, nature and society.

A bottle of glycerin purchased at a pharmacy

Glycerol

Simple polyol compound.

Simple polyol compound.

A bottle of glycerin purchased at a pharmacy
Personal lubricants commonly contain glycerol
Glycerol is an ingredient in products such as hair gel
Glycerol suppositories used as laxatives
Glycerin is often used in electronic cigarettes to create the vapor

Owing to the presence of three hydroxyl groups, glycerol is miscible with water and is hygroscopic in nature.

In a system at thermal equilibrium, neutrons (red) are elastically scattered by a hypothetical moderator of free hydrogen nuclei (blue), undergoing thermally activated motion. Kinetic energy is transferred between particles. As the neutrons have essentially the same mass as protons and there is no absorption, the velocity distributions of both particles types would be well-described by a single Maxwell–Boltzmann distribution.

Neutron moderator

Medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal kinetic energy.

Medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal kinetic energy.

In a system at thermal equilibrium, neutrons (red) are elastically scattered by a hypothetical moderator of free hydrogen nuclei (blue), undergoing thermally activated motion. Kinetic energy is transferred between particles. As the neutrons have essentially the same mass as protons and there is no absorption, the velocity distributions of both particles types would be well-described by a single Maxwell–Boltzmann distribution.
Fission cross section, measured in barns (a unit equal to 10−28 m2), is a function of the energy (so-called excitation function) of the neutron colliding with a 235U nucleus. Fission probability decreases as neutron energy (and speed) increases. This explains why most reactors fueled with 235U need a moderator to sustain a chain reaction and why removing a moderator can shut down a reactor.

Water (sometimes called "light water" in this context) is the most commonly used moderator (roughly 75% of the world's reactors).

Seawater off San Andrés

Seawater

Seawater off San Andrés
Temperature-salinity diagram of changes in density of water
Ocean salinity at different latitudes in the Atlantic and Pacific
Annual mean sea surface salinity expressed in the Practical Salinity Scale for the World Ocean. Data from the World Ocean Atlas
Diagram showing concentrations of various salt ions in seawater. The composition of the total salt component is: 55%, 30.6%,  7.7%,  3.7%,  1.2%,  1.1%,
Other 0.7%. Note that the diagram is only correct when in units of wt/wt, not wt/vol or vol/vol.

Seawater, or salt water, is water from a sea or ocean.

Sequence of reclamation from left: raw sewage, sewage treatment plant effluent, and finally reclaimed water (after several treatment steps)

Reclaimed water

Process of converting municipal wastewater (sewage) or industrial wastewater into water that can be reused for a variety of purposes.

Process of converting municipal wastewater (sewage) or industrial wastewater into water that can be reused for a variety of purposes.

Sequence of reclamation from left: raw sewage, sewage treatment plant effluent, and finally reclaimed water (after several treatment steps)
Irrigation water is pumped from this tank which stores effluent received from a constructed wetland in Haran-Al-Awamied, Syria.
Reclaimed water sign in Dunedin, United States
A lavender-colored pipeline carrying non-potable water in a dual piping system in Mountain View, California, U.S.
Uses of recycled water in California, 2011

Human urine and feces are input into one end of the reactor and pure oxygen, pure water, and compost (humanure) are output from the other end.

The Central Arizona Project Aqueduct transfers untreated water

Water supply network

Water supply networks are often run by public utilities of the water industry.

Water supply networks are often run by public utilities of the water industry.

The Central Arizona Project Aqueduct transfers untreated water
Most (treated) water distribution happens through underground pipes
Pressurizing the water is required between the small water reserve and the end-user
Clean drinking water is essential to human life.
Sustainable development in an urban water network

Water is an essential natural resource for human existence.

Four exoplanets orbiting counterclockwise with their host star (HR 8799).

Exoplanet

Planet outside the Solar System.

Planet outside the Solar System.

Four exoplanets orbiting counterclockwise with their host star (HR 8799).
Exoplanet HIP 65426b is the first discovered planet around star HIP 65426.
Coronagraphic image of AB Pictoris showing a companion (bottom left), which is either a brown dwarf or a massive planet. The data was obtained on 16 March 2003 with NACO on the VLT, using a 1.4 arcsec occulting mask on top of AB Pictoris.
Directly imaged planet Beta Pictoris b
Discovered extrasolar planets per year and by detection method (as of September 2014):
The Morgan-Keenan spectral classification
Artist's impression of exoplanet orbiting two stars.
This color–color diagram compares the colors of planets in the Solar System to exoplanet HD 189733b. The exoplanet's deep blue color is produced by silicate droplets, which scatter blue light in its atmosphere.
Clear versus cloudy atmospheres on two exoplanets.
Sunset studies on Titan by Cassini help understand exoplanet atmospheres (artist's concept).
Artist's illustration of temperature inversion in exoplanet's atmosphere.

Furthermore, a potentially habitable planet must orbit a stable star at a distance within which planetary-mass objects with sufficient atmospheric pressure can support liquid water at their surfaces.