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Article: Water
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- This article focuses on water as it is experienced in everyday life. See Water (molecule) for information on the chemical and physical properties of pure water, and Water (disambiguation) for other meanings.
Water (in its pure form) is a tasteless, odorless substance that is essential to all known forms of life and is known also as the universal solvent. It appears colorless to the naked eye in small quantities, though it can be seen to be blue in large quantities or with scientific instruments[1]. An abundant substance on Earth, water exists in many forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. Water in these bodies continuously moves through a cycle of evaporation, precipitation, and runoff to the sea. Clean water is essential to human health and in many parts of the world it is in short supply.
Etymology
The word "water" comes from the Old English wæter. The word is derived from the Proto-Indo-European language root *wod-or with other forms including *ud- and *wed-; the source of the word wet. This root is the source for words about water in many European language c.f German "Wasser", Latvian "ūdens" or Russian "вода" (voda).[2]
Chemical and physical properties
| Water | |
|---|---|
  | |
| General | |
| Systematic name | Water |
| Other names | Aqua Dihydrogen monoxide Hydrogen oxide |
| Molecular formula | H2O |
| Molar mass | 18.02 g/mol |
| Density and phase | 1000 kg/m3, liquid 917 kg/m3, solid |
| Melting point | 0 °C (273.15 K) (32ºF) |
| Boiling point | 100 °C (373.15 K) (212ºF) |
| Specific heat capacity (liquid) | 4186 J/(kg·K) |
| Disclaimer and references | |
Water has the chemical formula H2O meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. It can also be described ionically as HOH, with a hydrogen ion (H+) that is bonded to a hydroxide ion (OH-). It is in dynamic equilibrium between the liquid and vapor states at standard temperature and pressure. At room temperature, it is a nearly colorless, tasteless, and odorless liquid. It is often referred to in the sciences as the universal solvent and the only pure substance found naturally in all three states of matter.
Forms of water
- For more details on this topic, see Category: Forms of water.
Water takes many different forms on Earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers and rivers in the mountains, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle.
Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows.
Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers.
Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells.
Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.
Heat capacity and heat of vaporization
Water also has the highest specific heat capacity of any known chemical compound, as well as a high heat of vaporization, both due to the extensive hydrogen bonding between its molecules. These two unusual properties allows water to moderate Earth's climate by buffering large swings in temperature.
Color
Because water absorbs strongly in the infrared portion of the light spectrum, a small amount of visible red light is absorbed as well, resulting in water's slightly blue color when seen in mass quantities such as a lake or ocean. Its color can vary strongly depending on the minerals dissolved in it, for example limestone turns bodies of water turquoise, while iron compounds turn it red/brown and copper compounds create an intense blue.
Solvation
Water is a very good solvent, dissolving many types of substances, such as various salts and sugar. It facilitates chemical interactions such as the process of metabolism. Some substances, however, do not mix well with water, including lipids, some proteins and other hydrophobic substances. The chemical force explaining (among other things) why oil and water, famously, do not mix is Van der Waals force. Cell membranes take advantage of this property to carefully control interactions between their contents and external chemicals, which is facilitated somewhat by the surface tension of water. Substances dissolved in water are referred to as aqueous.
Cohesion and adhesion
Water sticks to itself (cohesion) because it is polar, meaning one end of the molecule has more slightly more negative charge than another (and vice-versa). In water, this happens because the oxygen atom is more electronegative - that is, it has a stronger "pulling power" on the molecule's electrons, drawing them closer (along with their negative charge), and making the area around the oxygen atom more negative than the area around both the hydrogen atoms.
Due to the polar nature of water, it is also very good at sticking to other things (adhesion).
Surface tension
Water has a high surface tension caused by the strong cohesion between water molecules. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces.
In biological cells and organelles, water is in contact with membrane and protein surfaces that are hydrophilic, that is, surfaces that have a strong attraction to water. Irving Langmuir observed a strong repulsive force between hydrophilic surfaces. To dehydrate hydrophilic surfaces—to remove the strongly held layers of water of hydration—requires doing substantial work against these forces, called hydration forces. These forces are very large, but decrease rapidly over a nanometer or less. Their importance in biology has been extensively studied by V. Adrian Parsegian of the NIH [3]. They are particularly important when cells are dehydrated by exposure to dry atmospheres or to extracellular freezing.
Capillary action
Capillary action refers to the process of water moving up a narrow tube against the force of gravity. It occurs because water adheres to the sides of the tube, and then more water is pulled on top of that water due to cohesion, which sticks to the sides of the tube. The process is repeated as the water flows up the tube until there is enough water that gravity can counteract the adhesive force.
Water's freezing point anomaly
A simple but environmentally important and unique property of water is that its common solid form, ice, floats on its liquid form. This solid phase is not as dense as liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is denser than the liquid form. Fresh water at standard atmospheric pressure is most dense at 4 °C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4 °C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up.
Electrical conductivity
A common misconception about water is that it is a powerful conductor of electricity, with risks of electrocution explaining this popular belief. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize where two water molecules become one hydroxide anion and one hydronium cation, but not enough to carry enough electric current to do any work or harm for most operations. Pure water can also be electrolyzed into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. The taste advertised in spring water or mineral water derives from the minerals present, while pure H2O is tasteless. As such, purity in spring and mineral water refers to purity from toxins, pollutants, and microbes.
The position of the Earth relating to water
Scientists theorize that most of the universe's water is produced as a byproduct of star formation. Gary Melnick, a scientist at the Harvard-Smithsonian Center for Astrophysics, explains: "For reasons that aren't entirely understood, when stars are born, their birth is accompanied by a strong outward wind of gas and dust. When this outflowing material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water we observe is rapidly produced in this warm dense gas." [4]
The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer to or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.
Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provide a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars).
The distance between Earth and the Sun, the combination of solar radiation received and the greenhouse effect of the atmosphere ensure that Earth's surface is neither too cold nor too hot for liquid water. If Earth were more distant from the Sun, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor.
It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.
Water's effect on life
From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. It carries out this role by allowing organic compounds to react in ways that ultimately allows replication. All known forms of life depend on water. Water is both vital as a solvent in which many of the bodies solutes dissolve, and an essential part of many metabolic processes within the body (e.g. significant quantities of water are used during the digestion of food).
Fresh water has its greatest density under normal atmospheric pressure at 4 °C, then becoming less dense as it freezes or heats up from this point - the only reason bodies of water do not freeze all the way through (which would kill all the organisms within it). As a stable, polar molecule prevalent in the atmosphere, it plays an important role as a greenhouse gas absorbing infrared radiation, without which, Earth's average surface temperature would be -18 °C.
Life forms that live in water
Earth's waters are filled with life. Fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales that also live in the water. Some types of animal, 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, however, is generally the foundation of the ocean food chain.
Different water creatures have found different solutions to obtaining oxygen in the water. Fish have gills instead of lungs, though some species of fish, such as the lungfish have both. Marine mammals, such as dolphins, whales, otters, and seals need to surface periodically to breath from the air.
Water in human civilization
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. Large metropolises like London, Montreal, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.
Human uses of water
Humans use water in a variety of ways. About 72% of the fat free mass of the human body is made of water. To function properly, the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water (hot tea being often used in deserts to avoid dehydration, etc.) It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which can be fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source [5]. There are other myths such as the effect of water on weight loss and constipation that have been dispelled [6]. The latest dietary reference intake report by the US National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men [7]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath.
Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as Vibrio. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.
In addition to drinking, water is valuable to humans due to its properties as a solvent. It is used to wash everything from the human body, clothes, floors, cars, food, pets, and just about everything else.
Water is also an important component of the cooking process. Most food should be washed prior to being cooked and eaten. Boiling, steaming, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam.
Water is also important in industrial contexts.
Recreational use of water
Humans use water for many recreational purposes, and for exercise, and in many sports. Some of these include swimming, waterskiing, boating, ice skating, skiing, fishing, and diving. In addition, the team sport, hockey is played on ice.
Lakesides and beaches are popular places for people to go to relax and enjoy recreation.
Water and human health
Water fit for human consumption is called drinking water or "potable water". Water that is not specifically made for drinking, but is not harmful for humans when used for food preparation is called safe water.
This natural resource is becoming scarcer in certain places, and its availability is a major social and economic concern.
Currently, about 1 billion people around the world routinely drink unhealthy water. Most countries have accepted the goal of halving by 2015 the number of people worldwide who do not have access to safe water and sanitation during the 2003 G8 Evian summit [8]. Even if this difficult goal is met, it will still leave more than an estimated half a billion people without access to safe drinking water supplies and over 1 billion without access to adequate sanitation facilities. Poor water quality and bad sanitation are killers; some 5 million deaths a year are caused by polluted drinking water.
That is hardly surprising, since in the developing world, 90% of all wastewater still goes untreated into local rivers and streams. Some 50 countries, with roughly a third of the world’s population, also suffer from medium or high water stress, and 17 of these extract more water annually than is recharged through their natural water cycles [citation needed]. The strain affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.
The politics of water distribution
- See water resources for information about fresh water supplies; see also Category:Water and politics for articles treating about water politics
Because of overpopulation in many regions of the world, mass consumption and water pollution, the availability of drinking water per capita is inadequate and shrinking as of the year 2006. For this reason, water is a strategic resource in the globe, and an important element in many political conflicts. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world. There is a long history of conflict over water, including efforts to gain access to water, the use of water in wars started for other reasons, and tensions over shortages and control [9]. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Fresh water, now more precious than ever in our history for its extensive use in agriculture, high-tech manufacturing, and energy production, is increasingly receiving attention as a resource requiring better management and sustainable use.
Water in the OECD countries
With nearly 2,000 cubic metres of water per person and per year, the United States leads the world in water consumption per capita (a large quantity of golf fields and car washing partly explain this massive consumption). In the Organisation for Economic Co-operation and Development (OECD) countries, the U.S. comes first for water consumption, then Canada with 1,600 cubic metres of water per person per year, which is about twice the amount of water used by the average person from France, three times as much as the average German, and almost eight times as much as the average Dane. Since 1980, overall water use in Canada has increased by 25.7%. This is five times higher than the overall OECD increase of 4.5%. In contrast, nine OECD nations were able to decrease their overall water use since 1980 (Sweden, the Netherlands, the United States, the United Kingdom, the Czech Republic, Luxembourg, Poland, Finland and Denmark) [10] [11].
Ninety-five percent of the United States' fresh water is underground. One crucial source is a huge underground reservoir, the 800-mile (1,300 km) Ogallala aquifer which stretches from Texas to South Dakota and waters one fifth of U.S. irrigated land. Formed over millions of years, the Ogallala aquifer has since been cut off from its original natural sources. It is being depleted at a rate of 12 billion cubic metres a year, amounting to a total depletion to date of a volume equal to the annual flow of 18 Colorado Rivers. Some estimates say it will dry up in as little as 25 years. Many farmers in the Texas High Plains, which rely particularly on the underground source, are now turning away from irrigated agriculture as they become aware of the hazards of overpumping [12].
Water in Mexico
In Mexico City, an estimated 40% of the city's water is lost through leaky pipes built at the turn of the century [13].
Water in the Middle East
The Middle East region has only 1% of the world's available fresh water, which is shared between 5% of the world's population. Thus, in this region, water is an important strategic resource. By 2025, it is predicted that the countries of the Arabian peninsula will be using more than double the amount of water naturally available to them [14]. According to a report by the Arab League, two-thirds of Arab countries have less than 1,000 cubic meters water per person per year, which is considered the limit [15].
Jordan, for example, has little water and dams in other countries have reduced its available water over the years. The 1994 Israel-Jordan Treaty of Peace stated that Israel would give 50 million cubic meters of water per year to Jordan, which it refused to do in 1999 before backtracking. The 1994 treaty stated that the two countries would cooperate in order to allow Jordan better access to water resources, notably through dams on the Yarmouk River [16]. Confronted by this lack of water, Jordan is preparing new techniques to use non-conventional water resources, such as second-hand use of irrigation water and desalinization techniques, which are very costly and are not yet used. A desalinization project will soon be started in Hisban, south of Amman. The Disi groundwater project, in the south of Jordan, will cost at least $250 million to bring out water. Along with the Unity Dam on the Yarmouk River, it is one of Jordan's largest strategic projects. Born in 1987, the "Unity Dam" would involve both Jordan and Syria. This "Unity Dam" still has not been implemented because of Israel's opposition, Jordan and Syrian conflictual relations and refusal of world investors. However, Jordan's reconciliation with Syria following the death of King Hussein represents the removal of one of the project's greatest obstacles. [17].
Both Israel and Jordan rely on the Jordan River, but Israel controls it, as well as 9/10 of the water resources in the region. Water is also an important issue in the conflict with the Palestinians - indeed, according to former Israeli prime minister Ariel Sharon quoted by Abel Darwish in the BBC, it was one of the causes of the 1967 Six-Day War. In practise the access to water has been a casus belli for Israel. The Israeli army prohibits Palestinians from pumping water, and settlers use much more advanced pumping equipment. Palestinians complain of a lack of access to water in the region [18]. Israelis in the West Bank use four times as much water as their Palestinian neighbours [19]. According to the World Bank, 90% of the West Bank's water is used by Israelis [17]. Article 40 of the appendix B of the September 28, 1995 Oslo accords stated that "Israel recognizes Palestinians' rights on water in the West Bank".
The Golan Heights provide 770 million cubic meters of water per year to Israel, which represents a third of its annual consumption. The Golan's table water goes to the Sea of Galilee, which is Israel's largest reserve, which is afterward redistributed throughout the country by the National Water Carrier. The Golan, which Israel annexed, represents, for Israel, a strategic territory because of its water resources. [17]. However, the level on the Sea of Galilee has dropped over the years, sparking fears that Israel's main water reservoir will become salinated. On its northern border, Israel threatened military action in 2002 when Lebanon opened a new pumping station taking water from a river feeding the Jordan. To help ease the crisis, Israel has agreed to buy water from Turkey and is investigating building desalination plants [20].
On the other hand, Iraq and Syria watched with apprehension the construction of the Atatürk Dam in Turkey and a projected system of 22 dams on the Tigris and Euphrates rivers [21]. According to the BBC, the list of 'water-scarce' countries in the region grew steadily from three in 1955 to eight in 1990 with another seven expected to be added within 20 years, including three Nile nations (the Nile is shared by nine countries).
Water in Asia
In Asia, Vietnam and Cambodia are concerned by China's and Laos' attempts to control the flux of water. China is also preparing the Three Gorges Dam project on the Yangtze River, which would become one of the world's largest dams, causing many social and environmental problems. It also has a project to divert water from the Yangtze to the dwindling Yellow River, which feeds China's most important farming region.
The Ganges is disputed between India and Bangladesh. The water reserves are being quickly depleted and polluted, while the glacier feeding the sacred Hindu river is retreating hundreds of feet each year because of global warming and deforestation in the Himalayas causing subsoil streams flowing into the Ganges river to dry up. Downstream, India controls the flow to Bangladesh with the Farakka Barrage, 10 km on the Indian side of the border. Until the late 1990s, India used the barrage to divert the river to Calcutta to stop the city's port drying up during the dry season. This denied Bangladeshi farmers water and silt, and left the Sundarban wetlands and mangrove forests at the river's delta seriously threatened. The two countries have now signed an agreement to share the water more equally. Water quality, however, remains a huge problem, with high levels of arsenic and untreated sewage in the river water [22].
Water in South America
The Guaraní Aquifer, located between the Mercosur countries of Argentina, Brazil, Bolivia and Paraguay, with a volume of about 40000 km³, is an important source of fresh, drinkable water, for all four countries.
Privatisation of water companies
Privatisation of water companies has been contested on several occasions, due to bad quality of the water, increasing prices, etc. In Bolivia for example, the proposed privatization of water companies by the IMF were met by popular protests in Cochabamba in 2000, which ousted Bechtel, an American engineering firm based in San Francisco. SUEZ has started retreating from South America, due to similar protests (in Buenos Aires in Argentina, as well as in Santa Fe; in Córdoba, consumers took to the streets to protest water rate hikes of as much as 500 percent mandated by Suez). In South and Central America, Suez has water concessions in Argentina, Bolivia, Brazil and Mexico. "Bolivian officials fault Suez for not connecting enough households to water lines as mandated by its contract and for charging as much as $455 a connection, or about three times the average monthly salary of an office clerk", according to the Mercury News [23]. South Africa also made moves to privatize water, provoking an outbreak of cholera killing 200 [24].
Regulating water distribution
Drinking water is often collected at springs, extracted from artificial borings in the ground, or wells. 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 are rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve 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 ocean or seawater is a more expensive solution used in coastal arid climates.
The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs.
Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the polluter. As other types of pollution, this does not enter standard accounting of market costs, being conceived as externalities for which the market can not account for. Thus other people pay the price of this water pollution, while the private firms' profits are not redistributed to the local population victim of this pollution. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.
The impact of water on religion and philosophy
Water is considered a purifier in most religions, including Hinduism, Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the five daily prayers can be done only after completing washing the body with clean water (wudu). In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is mentioned in the Bible 442 times in the New International Version and 363 times in the King James Version: 2 Peter 3:5(b) states, "The earth was formed out of water and by water" (NIV).
Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess, while Saraswati have been referred to as goddess in Vedas. Also water is one of the "panch-tatva"s (basic 5 elements, others including fire, earth, space, air). Alternatively, gods can be patrons of particular springs, rivers, or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids.
The 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. Water was considered cold and moist. In the theory of the four bodily humors, water was associated with phlegm. Water was also one of the five elements in traditional Chinese philosophy, along with earth, fire, wood, and metal.
See also
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