Common Definitions of Water

Water – noun

Water is the liquid that descends from the clouds as rain, forms streams, lakes, and seas, and is a major constituent of all living matter and that when pure is an odorless, tasteless, very slightly compressible liquid oxide of hydrogen H2O which appears bluish in thick layers, freezes at 0° C and boils at 100° C, has a maximum density at 4° C and a high specific heat, is feebly ionized to hydrogen and hydroxyl ions, and is a poor conductor of electricity and a good solvent.

Our water is the clear liquid that has no color, taste, or smell, that falls from clouds as rain, that forms streams, lakes, and seas, and that is used for drinking, washing, etc.


The propensity of water to form solutions and emulsions is useful in various washing processes. Washing is also an important component of several aspects of personal bodyhygiene. Most of the personal water use is due to showering, doing the laundry and dishwashing, reaching hundreds of liters per day per person in developed countries.

You can pour water on the earth to feed plants or to give a cow water to drink.

It comes out of our eyes if we are happy or sad. This is called tears.

The sea is the part of the earth covert with water. We can travel or transportation on water we went by water. We are the water, so we have a watery fluid (such as tears, urine, or sap) formed or circulating in a our bodies.

Important Water Facts 

 Water is the main compound found in living organisms. Approximately 62 percent of the human body is water.

 In its liquid form, water is transparent and nearly colorless. Large volumes of liquid water and ice are blue. The reason for the blue color is the weak absorption of light at the red end of the visible spectrum. Pure water is flavorless and odorless.

About 71 percent of the Earth’s surface is covered by water. Breaking it down, 96.5 percent of the water in the Earth’s crust is found in oceans, 1.7 percent in ice caps and glaciers, 1.7 percent in groundwater, a small fraction in rivers and lakes, and 0.001 percent in clouds, water vapor, and precipitation.

Only about 2.5 percent of the Earth’s water is freshwater. Nearly all of that water (98.8 percent) is in ice and groundwater.Water is the third most abundant molecule in the universe, after hydrogen gas (H2) and carbon monoxide (CO). The chemical bonds between hydrogen and oxygen atoms in a water molecule are polar covalent bonds. Water readily forms hydrogen bonds with other water molecules. One water molecule may participate in a maximum of four hydrogen bonds with other species.

Water has an extraordinarily high specific heat capacity [4.1814 J/(g·K) at 25 degrees C] and also a high heat of vaporization [40.65 kJ/mol or 2257 kJ/kg at the normal boiling point]. Both of these properties are a result of hydrogen bonding between neighboring water molecules.

Water is nearly transparent to visible light and the regions of the ultraviolet and infrared spectrum near the visible range. The molecule absorbs infrared light, ultraviolet light, and microwave radiation.

Water is an excellent solvent because of its polarity and high dielectric constant. Polar and ionic substances dissolve well in water, including acids, alcohols, and many salts. Water displays capillary action because of its strong adhesive and cohesive forces. Hydrogen bonding between water molecules also gives it high surface tension. This is the reason why small animals and insects can walk on water. Pure water is an electrical insulator. However, even deionized water contains ions because water undergoes auto-ionization. Most water contains trace amounts of solute. Often the solute is salt, which dissociates into ions and increases the conductivity of water. The density of water is about one gram per cubic centimeter. Regular ice is less dense than water and floats on it. Very few other substances exhibit this behavior. Paraffin and silica are other examples of substances that form lighter solids than liquids. The molar mass of water is 18.01528 g/mol.

The melting point of water is 0.00 degrees C (32.00 degrees F; 273.15 K). Note the melting and freezing points of water may be different from each other. Water readily undergoes supercooling. It can remain in a liquid state well below its melting point. 

The boilingpoint of water is 99.98 degrees C (211.96 degrees F; 373.13 K).

Water is amphoteric. In other words, it can act as both an acid and as a base.


We also moisten, sprinkle, or soak with water water the lawn

If you have a farm you need to supply the cattle with water to drink.

Some lands are watered by the river

Would you like a glass of water? There’s water dripping from the ceiling.

Water is the liquid that descends from the clouds as rain, forms streams, lakes, and seas, and is a major constituent of all living matter and that is an odorless, tasteless, very slightly compressible liquid oxide of hydrogen H2O which appears bluish in thick layers, freezes at 0°C (32°F) and boils at 100°C (212°F), has a maximum density at 4°C (39°F) and a high specific heat, is feebly ionized to hydrogen and hydroxyl ions, and is a poor conductor of electricity and a good solvent.

Water is a good polar solvent, that dissolves many salts and hydrophylic organic molecules such as sugars and simple alcohols such as ethanol. Water also dissolves many gases, such as oxygen and carbon dioxide -the latter giving the fizz of carvonated beverages, sparcling whines and beers. In addition, many substances in living organisms, such as proteins, DNA and polysaccharides, are dissolved in water. The interactions between water and the subunits of these biomacromolecules shape proteinfolding, DNA base pairing, and other phenomena crucial to life (hydrophobic effect).

Many organic substances (such as fats and oils and alkanes) are hydrophonic, that is, insoluble in water. Many inorganic substances are insoluble too, including most metal oxides, sulfides, and silicates.

A clear, colorless, odorless, and tasteless liquid essential for most plant and animal life and the most widely used of all solvents. Freezing point 0°C (32°F); boiling point 100°C (212°F); specific gravity (4°C) 1.0000; weight per gallon (15°C) 8.338 pounds (3.782 kilograms).

Any of the liquids that are present in or passed out of the body, such as urine, perspiration, tears, or saliva.

The fluid that surrounds a fetus in the uterus; amniotic fluid.

An aqueous solution of a substance, especially a gas.

A pharmaceutical or cosmetic preparation made with water is also called tea.

If you are above water, out of embarrassment or trouble, especially of a financial nature: They had so many medical bills that they could hardly keep their heads above water.

Swimm and break water to break the surface of the water by emerging from it. To break the surface of the water with the feet, especially in swimming the breaststroke doing the frog kick. With Medicine  break the amniotic sac prior to parturition.

Origin of the word water

Sami: Čáhci,

First recorded before 900; Middle English wæter, watre, water, Old English noun wæter, uæt(t)er; cognate with Dutch water, German Wasser; akin to Old Norse vatn, vatr Gothic wato, Hittite watar, Greek hýdōr; Middle English watere(n), Old English verb wæterian, wetrian “to give water to, irigate, moisten,” derivative of the noun, slovenian: voda

Old English wæter, of Germanic origin; compare Old Saxon watar, Old High German wazzar, Gothic watō, Old Slavonic voda; related to Greek hudor

The word water comes from Old English wæter, from Proto-Germanic *watar (source also of Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, GermanWasser, vatn, Gothic 𐍅𐌰𐍄𐍉 (wato), from Proto Indo European *wod-or, suffixed form of root *wed- („water“; „wet“). Also cognate, through the Indo-European root, with Greek ύδωρ (ýdor), Russianвода́ (vodá), Irish uisce, and Albanian ujë Rätoromanisch Ava

The word „water“ comes from the Old English word wæter or from the Proto-Germanic watar or German Wasser. All of these words mean „water“ or „wet.“

Old English wæter (noun), wæterian (verb), of Germanic origin; related to Dutch water, German Wasser, from an Indo-European root shared by Russian voda (compare with vodka), also by Latin unda ‘wave’ and Greek hudōr ‘water’.

Water: 1. A tasteless odorless colorless liquid with the chemical formula H2O.
2. The liquid which forms rain, rivers, and the sea and makes up a large part of the bodies of most organisms, including humans.
3. The amniotic fluid, as in the bag of waters.
4. The cerebrospinal fluid, especially under increased pressure, as in water on the brain.

Here are a few examples how we use the word water in everyday laguage:

As a noun:


    •  One of the four elements in ancient and medieval philosophy and in astrology (considered essential to the nature of the signs Cancer, Scorpio, and Pisces) as modifier ‘a water sign’
    •  usually the waters The water of a mineral spring as used medicinally for bathing in or drinking.‘resorts where southerners came to take the waters’
    •  with modifier A solution of a specified substance in water. ‘ammonia water’ 
    •  the water A stretch or area of water, such as a river, sea, or lake ‘the lawns ran down to the water’s edge’
    • The surface of an area of water.‘she ducked under the water’
    •  as modifier Found in, on, or near areas of water.
    •   waters The water of a particular sea, river, or lake.the waters of Hudson Bay’
    •  waters An area of sea regarded as under the jurisdiction of a particular country. Japanese coastal waters’
    • Urine.
    •  waters The amniotic fluid surrounding a fetus in the womb, especially as discharged in a flow shortly before birth.I think my waters have broken’
    •  The quality of transparency and brilliance shown by a diamond or other gem.
    •  Finance : Capital stock that represents a book value greater than the true assets of a company.
as a verb
    •  with object Pour or sprinkle water over (a plant or area) in order to encourage plant growth.‘I went out to water the geraniums’


    • Give a drink of water to (an animal)they stopped to water the horses and to refresh themselves’
    • (of a river) flow through (an area of land)the valley is watered by the Pines River’
    •  Take a fresh supply of water on board (a ship or steam train) ‚the ship was watered and fresh livestock taken aboard’
    • no object (of the eyes) become full of moisture or tears.‘Rory blinked, his eyes watering’
    • (of a person’s mouth) produce saliva, typically in response to the sight or smell of appetizing food.‘the smell of frying bacon made Hilary’s mouth water’
    • with object Dilute or adulterate (a drink, typically an alcoholic one) with water.staff at the club had been watering down the drinks’
    • water something down Make a statement or proposal less forceful or controversial by changing or leaving out certain details. ‘the army’s report of its investigation was considerably watered down
    • Finance  Increase (a company’s debt, or nominal capital) by the issue of new shares without a corresponding addition to assets.
or in Phrases

like water

      •  In great quantities. George was spending money like water’
    •  by water Using a ship or boat for travel or transport.
      ‘at the end of the lake was a small gazebo, accessible only by water’
    •  make water Urinate.‘A woman enters the bathroom with the desire/need to make water or to poop.’
    •  Two(of a ship or boat) take in water through a leak. 

    • the water of life = Whiskey. Or is this a clumsy attempt at a makeover for the water of life, something based on the London vodka restaurants that once revolutionised the perception of Russia’s finest?’

    • pass water, Urinate.
    •  water on the brain informal Hydrocephalus.
    •  of the first water 1(of a diamond or pearl) of the greatest brilliance and transparency.

      (typically of someone or something perceived as undesirable or annoying) extreme or unsurpassed of their kind.she was a bore of the first water’

    • water under the bridge

    •  sed to refer to events or situations that are in the past and consequently no longer to be regarded as important or as a source of concern. Past fiscal decisions are water over the dam, given the national government’s priority for addressing recession in a timely manner.’




Water industry

The water industry provides drinking water and wastewater services (including sewage treatment) to households and industry. Water supply facilities include water wells, cisterns for rainwater harwesting, water supply networks, and water purification facilities, water tanks, water towers, water pipes including old aqueducts. Atmospheric water generators are in development.

Drinking water is often collected at springs, extracted from artificial borings (wells) in the ground, or pumped from lakes and rivers. Building more wells in adequate places is thus a possible way to produce more water, assuming the aquifers can supply an adequate flow. Other water sources include rainwater collection. Water may require purification for human consumption. This may involve the removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material, while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant seawater is a more expensive solution used in coastal arid.

The distribution of drinking water is done through muncipal water systems, tanker delivery or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge.

Reducing usage by using drinking (potable) water only for human consumption is another option. In some cities such as Hong Kong, seawater is extensively used for flushing toilets citywide in order to converse freshwater recources.

Water in Religion

People come to Inda Abba Hadera spring (India Sillasie, Ethiopia) to wash in holy water

Water is considered a purifier in most religions. Faiths that incorporate ritual washing (ablution) include Christianity, Hinduism, Islam, Judaism, the Rastafari movement, Shinto, Taoism and Wicca. Immersion (or aspersion or affusion) of a person in water is a central sacrament of Christianity (where it is called babtism); it is also a part of the practice of other religions, including Islam (Ghusl), Judaism (mikvah) and Sikhism (Amrit Sanskar). In addition, a ritual bath in pure water is performed for the dead in many religions including Islam and Judaism. In Islam, the five daily prayers can be done in most cases after completing washing certain parts of the body using clean water (wudu), unless water is unavailable. In Shinto, water is used in almost all rituals to cleanse a person or an area.

In Christianity, holy water is water that has been sanctified by a priest for the purpose of baptism, the blessing of persons, places, and objects, or as a means of repelling evil.

In Zoroastrism, water (ab) is respected as the source of life.

Water in Philosophy

The Ancient Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic substance of the universe. Thales, who was portrayed by Aristotle as an astronomer and an engineer, theorized that the earth, which is denser than water, emerged from the water. Thales, a monist, believed further that all things are made from water. Plato believed the shape of water is an icosahedron which accounts for why it is able to flow easily compared to the cube-shaped earth.

In the theory of the four bodily humors, water was associated with phlegm, as being cold and moist. The classical element of water was also one of the five elements in traditional Chinese philosophy, along with earth, fire, wood and metal.

Water is also taken as a role model in some parts of traditional and popular Asian philosophy. James Legge‘s 1891 translation of the Dao de Jing states, „The highest excellence is like (that of) water. The excellence of water appears in its benefiting all things, and in its occupying, without striving (to the contrary), the low place which all men dislike. Hence (its way) is near to (that of) the Tao“ and „There is nothing in the world more soft and weak than water, and yet for attacking things that are firm and strong there is nothing that can take precedence of it—for there is nothing (so effectual) for which it can be changed.“Guanzi in the „Shui di“ 水地 chapter further elaborates on the symbolism of water, proclaiming that „man is water“ and attributing natural qualities of the people of different Chinese regions to the character of local water resources.

Art and activism

Painter and activist Fredericka Foster curated The Value of Water, at the Cathedral of St. John the Divine in New York City, which anchored a year long initiative by the Cathedral on our dependence on water. .



Land and Water

The soil is also very dry, which counterintuitively makes it harder for water to infiltrate.What’s more, the wetlands would prevent some of that water from moving inland, so flood levels around those homes would rise higher.

It is a clear colourless tasteless odourless liquid that is essential for plant and animal life and constitutes, in impure form, rain, oceans, rivers, lakes, etc. It is a neutral substance, an effective solvent for many compounds, and is used as a standard for many physical properties. Formula:

    •  Dihydrogen monoxide or DHMO
    •  Hydrogen hydroxide (HH or HOH)
    •  H2O
    • Hydrogen monoxide
    •  Dihydrogen oxide
    •  Hydric acid
    •  Hydrohydroxic acid
    •  Hydrol
    •  Hydrogen oxide

The polarized form of water, H+ OH, is called hydron hyroxide. H 2 O

Two hydrogen atoms are attached to one oxygen atom at an angle of 104.45°. The hydrogen atoms are close to two corners of a tetrahedron centered on the oxygen. At the other two corners are lone pairs of valence electrons that do not participate in the bonding. In a perfect tetrahedron, the atoms would form a 109.5° angle, but the repulsion between the lone pairs is greater than the repulsion between the hydrogen atoms.

Water (Chemical Formula: H2O) refers to a chemical substance consisting of two hydrogen atoms attached to the central oxygen atom via a covalent bond. This configuration results in a molecule that is polar. Since a water molecule is polarized, the electropositive hydrogen of one water molecule is electrostatically attracted to the electronegative oxygen atom of the nearby water molecule. The electrostatic dipole-dipole interaction between water molecules is called hydrogen bond.

The transient hydrogen bonds between water molecules form a transparent, colorless, odorless, and tasteless liquid. Apart from liquid, water may also occur in other forms such as gas (as water vapor) and solid (as ice). The hydrogen bonds between water molecules are responsible for the water’s distinctive properties, such as high boiling point (100 °C), high surface tension, specific heat, and heat of vaporization.1



Water differs from most liquids in that it becomes less dense as it freezes. In 1 atm pressure, it reaches its maximum density of 1,000 kg/m3 (62.43 lb/cu ft) at 3.98 °C (39.16 °F). The density of ice is 917 kg/m3 (57.25 lb/cu ft), an expansion of 9%. This expansion can exert enormous pressure, bursting pipes and cracking rocks.

In a lake or ocean, water at 4 °C (39.2 °F) sinks to the bottom, and ice forms on the surface, floating on the liquid water. This ice insulates the water below, preventing it from freezing solid. Without this protection, most aquatic organisms would perish during the winter.


Related adjective: aqueous Related combining forms: hydro-, aqua-

any body or area of this liquid, such as a sea, lake, river, etc
(as modifier)water sports; water transport; a water plant Related adjective: aquatic

„Water“ is the name of the liquid state of H2O at standard ambient temperature and pressure. It comes in the form of rain and gas in the form of fog. Clouds are formed from suspended droplets of water and ice its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or fog. Water moves continually through the water cycle of evaporation, transpiration, condensation, precipitation and runoff, usually reaching the sea.


Attention: here I found 2 different Opinions, the difference sounds interesting.

Water covers 71% of the Earth surface, mostly in seas and oceans. Small portions of water occur as groundwater (1,7%), in the glaciers and the ice caps of Antarctica and Grennland (1,7%), and in the air as vapor, clouds (formed of ice and liquid water suspended in air), and precipitation (0,001%)

Water covers 71% of the Earth’s surface; the oceans contain 96.5% of the Earth’s water. The Antarctic Ice Shield which contains 61% of all freshwater on Earth, is visible at the bottom. Condensed atmospheric water can be seen as clouds, contributing to the Earth’s albedo.


Water plays an important role in the world economy. Approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a major source of food for many parts of the world. Much of the long-distance trade of commodities (such as oil, natural gas, and manufactured products) is transported by boats through seas, rivers, lakes, and canals. Large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a wide variety of substances both mineral and organic; as such it is widely used in industrial processes, and in cooking and washing. Water, ice and snow are also central to many sports and other forms of entertainment, such as swimming, pleasureboating, boat racing, surfing, sport fishing, diving, ice skating and skiing.


Phase transitions

At a pressure of one atmosphere (atm), ice melts or water freezes at 0 °C (32 °F) and water boils or vapor condenses at 100 °C (212 °F). However, even below the boiling point, water can change to vapor at its surface by evaporation (vaporization throughout the liquid is known as boiling). Sublimation and deposition also occur on surfaces. For example, frost is deposited on cold surfaces while snowflakes form by deposition on an aerosol particle or ice nucleus. In the process of freeze-drying , a food is frozen and then stored at low pressure so the ice on its surface sublimates.

The melting and boiling points depend on pressure. A good approximation for the rate of change of the melting temperature with pressure is given by the Clausius-Clapeyron relation:

where and are the molar volumes of the liquid and solid phases, and is the molar latent heat of melting. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases. In glaciers, pressure melting can occur under sufficiently thick volumes of ice, resulting in subglacial lakes.

The Clausius-Clapeyron relation also applies to the boiling point, but with the liquid/gas transition the vapor phase has a much lower density than the liquid phase, so the boiling point increases with pressure. Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed 205 °C (401 °F) in Old Faithful , a geyser in Yellostone National Park. In hydrothermal vents, the temperature can exceed 400 °C (752 °F).

At sea level, the boiling point of water is 100 °C (212 °F). As atmospheric pressure decreases with altitude, the boiling point decreases by 1 °C every 274 meters. High altidude cooking takes longer than sea-level cooking. For example, at 1,524 metres (5,00 ft), cooking time must be increased by a fourth to achieve the desired result. (Conversely, a pressure cooker can be used to decrease cooking times by raising the boiling temperature. ) In a vacuum, water will boil at room temperature.

Electrical conductivity and electrolysis

Pure water has a low electrical conductivity, which increases with the dissolution of a small amount of ionic material such as common salt.

Liquid water can be split into the elemtens hydrogen and oxygen by passing an electric current through it—a process called electrolysis. The decomposition requires more energy input than the heat release by the inverse process (285.8 kJ/mol or 15.9 MJ/kg).

Mechanical properties

Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to 5.1×10−10 Pa−1 in ordinary conditions. Even in oceans at 4 km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume.

The viscosity of water is about 10−3 Pa·s or 0.01 poise at 20 °C (68 °F), and thespeed of sound in liquid water ranges between 1,400 and 1,540 meters per second (4,600 and 5,100 ft/s) depending on temperature. Sound travels long distances in water with little attenuation, especially at low frequencies (roughly 0.03 dB/km for 1 kHz), a property that is exploited by cetaceans and humans for communication and environment sensing (sonar).


Metallic elements which are more electropositive than hydrogen, particularly the alkali metals and alkaline earth metals such as lithium, sodium, calcium, potassium and cesium displace hydrogen from water, forming hydroxides and releasing hydrogen. At high temperatures, carbon reacts with steam to form carbon monoxide and hydrogen.

The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.

Water moves perpetually through each of these regions in the water cycle consisting of the following transfer processes:

    •  evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into the air.
    •  precipitation, from water vapor condensing from the air and falling to the earth or ocean.
    • runoff from the land usually reaching the sea.

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life. It carries out this role by allowing organic compounds to react in ways that ultimately allow replication . All known forms of life depend on water. Water is vital both as a solvent in which many of the body’s solutes dissolve and as an essential part of many metabolic processes within the body. Metabolism is the sum total of anabolism and catabolism. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g., starches, triglycerides, and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g., glucose, fatty acids, and amino acids to be used for fuels for energy use or other purposes). Without water, these particular metabolic processes could not exist.

Water is fundamental to photosynthesis and respiration. Photosynthetic cells use the sun’s energy to split off water’s hydrogen from oxygen. Hydrogen is combined with CO2 (absorbed from air or water) to form glucose and release oxygen. All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun’s energy and reform water and CO2 in the process (cellular respiration).

Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H+, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as a hydroxide ion (OH) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7. Acids have pH values less than 7 while bases have values greater than 7.

Aquatic life forms

Further information: Hydrobiology, Marine life, and Aquatic plant

Earth surface waters are filled with life. The earliest life forms appeared in water; nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales. Some kinds of animals, such as amphibians, spend portions of their lives in water and portions on land. Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton is generally the foundation of the ocean food chain.

Aquatic vertebrates must obtain oxygen to survive, and they do so in various ways. Fish have gills instead of lungs, although some species of fish, such as the lungfish, have both. Marine mammals , such as dolphins, whales, otters, and seals need to surface periodically to breathe air. Some amphibians are able to absorb oxygen through their skin. Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see insect and mollusc siphons) and gills (Carcinus. However, as invertebrate life evolved in an aquatic habitat most have little or no specialization for respiration in water.

Biological Importance

Water is one of the substances essential to life. Biomolecules (e.g. DNA, proteines, and polysaccharides), gases, vitamins, etc. are dissolved in water. The water may act as a transport medium to convey these substances to various parts of the body. It also acts as an important reactant in certain biochemical processes.

In plants, water is an essential requirement in photosynthesis. Since water molecules are polar, they can form transient hydrogen bonds between them and thereby help in the formation of biomolecular structures such as DNA and proteins. It is also because of the water’s polarity that it can interact with ions and other polar molecules.

Water is also important in dissociating compounds into ions. Thus, it helps regulate pH levels. Molecules or substances that are readily soluble in water are described as hydrophilic. Conversely, those that are not readily soluble in water are described as hydrophobic. They are said to be nonpolar and water does not readily dissolve them. The interactions of water with polar and nonpolar molecules are crucial to the function and structure of the lipid-bilayer plasma membrane. Water molecule is the most abundant molecule inside a cell, accounting for about 70% or more of the total cell mass.2 The cell contains water (together with ions, solutes, and other molecules) in its cytosol.

The water content of a human body is referred to as body water. It occurs in the tissues, such as

bones, muscles, adipose, blood and practically everywhere. The average adult human body is about 50 to 60 % water. The body of a newborn Infant contains a higher water percentage (as much as 93% of the bodyweight). The body water in humans (and in animals, too) is contained in various bodily fluids, i.e. extracellular fluid and intracellular fluid.

The extracellular fluid is that which is contained in body areas outside of cells and constitutes 1/3 of the body water. The intracellular fluids are those found inside the cells. They constitute about 2/3 of the body water.

Water on earth is also abundant. It exists as solid, liquid, or gas. About 70% of the Earth’s surface is water. Bodies of water on Earth serve as important habitats for aquatic organisms and a source of water for terrestrial living things. Three major types of aquatic habitats are marine water, freshwater, and brackish water.

Civilization has historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, was situated between the major rivers Tigris and Euphrates; the ancient society of the Egyptians depended entirely upon the Nile. The early Indus Valley Civilization (c. 3300 BCE to 1300 BCE) developed along the Indus River and tributaries that flowed out of the Himalayas. Rome was also founded on the banks of the Italian river Tiber. Large metropolises like Rotterdam, London, Montreal, Paris, New York City, Buenos Aires, Shanghai, Tokyo, Chicago, and Hong Kong owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore, have flourished for the same reason. In places such as North Africa and the Middle East, where water is more scarce, access to clean drinking water was and is a major factor in human development.


The most substantial human use of water is for agriculture, including irrigated agriculture, which accounts for as much as 80 to 90 percent of total human water consumption. In the United States, 42% of freshwater withdrawn for use is for irrigation, but the vast majority of water „consumed“ (used and not returned to the environment) goes to agriculture.

Access to fresh water is often taken for granted, especially in developed countries that have build sophisticated water systems for collecting, purifying, and delivering water, and removing wastewater. But growing economic, demographic, and climatic pressures are increasing concerns about water issues, leading to increasing competition for fixed water resources, giving rise to the concept of peak water. As populations and economies continue to grow, consumption of water-thirsty meat expands, and new demands rise for biofuels or new water-intensive industries, new water challenges are likely.

An assessment of water management in agriculture was conducted in 2007 by the International Water Management Institute in Sri Lanka to see if the world had sufficient water to provide food for its growing population. It assessed the current availability of water for agriculture on a global scale and mapped out locations suffering from water scarcity. It found that a fifth of the world’s people, more than 1.2 billion, live in areas of physical water scarcity, where there is not enough water to meet all demands. A further 1.6 billion people live in areas experiencing economic water scarcity, where the lack of investment in water or insufficient human capacity make it impossible for authorities to satisfy the demand for water. The report found that it would be possible to produce the food required in the future, but that continuation of today’s food production and environmental trends would lead to crises in many parts of the world. To avoid a global water crisis, farmers will have to strive to increase productivity to meet growing demands for food, while industries and cities find ways to use water more efficiently.

Water scarcity is also caused by production of water intensive products. For example, cotton: 1 kg of cotton—equivalent of a pair of jeans—requires 10.9 cubic meters (380 cu ft) water to produce. While cotton accounts for 2.4% of world water use, the water is consumed in regions that are already at a risk of water shortage. Significant environmental damage has been caused: for example, the diversion of water by the former Soviet Union from the Amu Darya and [[Syr Darya] rivers to produce cotton was largely responsible for the disappearance of the Aral Sea.

An original recommendation for water intake in 1945 by the Food and Nutrition Board of the

United Sates National Research Council read: „An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods.“ The latest dietary reference intake report by the United States National Research Council in general recommended, based on the median total water intake from US survey data (including food sources): 3.7 liters (0.81 imp gal; 0.98 U.S. gal) for men and 2.7 liters (0.59 imp gal; 0.71 U.S. gal) of water total for women, noting that water contained in food provided approximately 19% of total water intake in the survey.

Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. The Institute of Medicine (US) recommends that, on average, men consume 3 liters (0.66 imp gal; 0.79 U.S. gal) and women 2.2 liters (0.48 imp gal; 0.58 U.S. gal); pregnant women should increase intake to 2.4 liters (0.53 imp gal; 0.63 U.S. gal) and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing. Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

Humans require water with few impurities. Common impurities include metal salts and oxides, including copper, iron, calcium and lead, and/or harmful bacteria, such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.

Chemical uses

Water is widely used in chemical reactions as a sorvent or reactant and less commonly as a solute or catalyst. In inorganic reactions, water is a common solvent, dissolving many ionic compounds, as well as other polar compounds such as ammonia and compounds closely related to water. In organic reactions, it is not usually used as a reaction solvent, because it does not dissolve the reactants well and is amphoteric (acidic and basic) and nucleophilic. Nevertheless, these properties are sometimes desirable. Also, acceleration of Diels-Alder reactions by water has been observed. Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently. Water vapor is used for some processes in the chemical industry. An example is the production of acrylic acid from acrolein, propylene and propane. The possible effect of water in these reactions includes the physical-, chemical interaction of water with the catalyst and the chemical reaction of water with the reaction intermediates.

Heat exchange

Water and steam are a common fluid used for heat exchange, due to its availability and high heat capacity, both for cooling and heating. Cool water may even be naturally available from a lake or the sea. It’s especially effective to transport heat through vaporization and condensation of water because of its large latent heat of vaporization. A disadvantage is that metals commonly found in industries such as steel and copper are oxidized faster by untreated water and steam. In almost all thermal power stations, water is used as the working fluid (used in a closed-loop between boiler, steam turbine, and condenser), and the coolant (used to exchange the waste heat to a water body or carry it away by evaporation in a cooling tower). In the United States, cooling power plants is the largest use of water.

In the nuclear power industry, water can also be used as a neutron moderator. In most nuclear reactors, water is both a coolant and a moderator. This provides something of a passive safety measure, as removing the water from the reactor also slows the nuclear reaction down. However other methods are favored for stopping a reaction and it is preferred to keep the nuclear core covered with water so as to ensure adequate cooling.

Fire considerations


Water is used for fighting wildfires.

Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguising fluid. The evaporation of water carries heat away from the fire. It is dangerous to use water on fires involving oils and organic solvents because many organic materials float on water and the water tends to spread the burning liquid.

Use of water in fire fighting should also take into account the hazards of a steam explosion, which may occur when water is used on very hot fires in confined spaces, and of a hydrogen explosion, when substances which react with water, such as certain metals or hot carbon such as coal, charcoal, or coke graphite, decompose the water, producing watergas.

Some metallic oxides, most notably those of alkali metals and alkaline earth metals, produce so much heat on reaction with water that a fire hazard can develop. The alkaline earth oxide quicklime is a mass-produced substance that is often transported in paper bags. If these are soaked through, they may ignite as their contents react with water.



Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming, waterskiing, boating, surfing and diving. In addition, some sports, like ice hockey and ice skating, are played on ice. Lakesides, beaches and water parks are popular places for people to go to relax and enjoy recreation. Many find the sound and appearance of flowing water to be calming, and fountains and other water features are popular decorations. Some keep fish and other flora and fauna inside aquariums or ponds for show, fun, and companionship. Humans also use water for snow sports i.e. skiing, sledding, snowmibiling or snowboarding which require the water to be frozen.

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