Impact from a water drop causes an upward "rebound" jet surrounded by circular
capillary waves.
'Water' is a common
chemical substance that is essential to all known forms of
life.
[1]
In typical usage, ''water'' refers only to its
liquid form or
state, but the substance also has a
solid state, ''
ice'', and a
gaseous state, ''
water vapor''. About 1,460
teratonnes (Tt) of water covers 71% of the
Earth's surface, mostly in oceans and other large water bodies, with 1.6% of water below ground in
aquifers and 0.001% in the
air as
vapor,
clouds (formed of solid and liquid water particles suspended in air), and
precipitation.
[2] Some of the Earth's water is contained within man-made and natural objects near the Earth's surface such as water towers, animal and plant bodies, manufactured products, and food stores.
Saltwater oceans hold 97% of surface water,
glaciers and polar
ice caps 2.4%, and other land surface water such as
rivers and
lakes 0.6%. Water moves continually through a
cycle of
evaporation or
transpiration,
precipitation, and
runoff, usually reaching the
sea. Winds carry water vapor over land at the same rate as runoff into the sea, about 36 Tt per year. Over land, evaporation and transpiration contribute another 71 Tt per year to the precipitation of 107 Tt per year over land. Some water is trapped for varying periods in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land. Clean, fresh water is essential to
human and other life. In many parts of the world, it is in short supply. Many
organic molecules as well as
salts,
sugars,
acids,
alkalis, and some
gases (especially
oxygen), are
soluble in water.
Beyond the Earth, a significant quantity of water is thought to exist underground on the planet
Mars, on the moons
Europa and
Enceladus, and on the
exoplanets known as
HD 189733 b[3] and
HD 209458 b.
[4]
Water covers 71% of the
Earth's surface; the
oceans contain 97.2% of the Earth's water. The
Antarctic ice sheet, which contains 90% of all fresh water on Earth, is visible at the bottom. Condensed atmospheric water can be seen as
clouds, contributing to the Earth's
albedo.
Chemical and physical properties
Main articles: Water (molecule)
Water is the
chemical substance with
chemical formula '
H2O': one
molecule of water has two
hydrogen atoms
covalently
bonded to a single
oxygen atom. Water is a tasteless, odorless liquid at
ambient temperature and pressure, and appears colorless in small quantities, although it has its own intrinsic very light blue hue. Ice also appears colorless, and water vapor is essentially invisible as a gas.
[5]
Water is primarily a liquid under standard conditions, which is not predicted from its relationship to other analogous hydrides of the
oxygen family in the
periodic table, which are gases such as
hydrogen sulfide. Also the elements surrounding oxygen in the
periodic table,
nitrogen,
fluorine,
phosphorus,
sulfur and
chlorine, all combine with
hydrogen to produce gases under standard conditions. The reason that oxygen hydride (water) forms a liquid is that it is more
electronegative than all of these elements (other than fluorine). Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom. The presence of a charge on each of these atoms gives each water molecule a net
dipole moment. Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore raising the boiling point. This attraction is known as
hydrogen bonding. Water can be described as a polar liquid that dissociates disproportionately into the
hydronium ion (H
3O
+(aq)) and an associated
hydroxide ion (OH
−(aq)).
Water is in
dynamic equilibrium between the
liquid,
gas and
solid states at
standard temperature and pressure, and is the only pure substance found naturally on Earth to be so.
Cohesion and adhesion
Water has a partial negative charge (σ-) near the oxygen atom due to the unshared pairs of electrons, and partial positive charges (σ+) near the hydrogen atoms. In water, this happens because the oxygen atom is more
electronegative than the hydrogen atoms — 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 of the hydrogen atoms.
Adhesion
Water sticks to itself (
cohesion) because it is
polar.
Water also has high
adhesion properties because of its polar nature. On extremely clean/smooth
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
National Institute of Health.
[6] They are particularly important when cells are dehydrated by exposure to dry atmospheres or to extracellular freezing.
Surface tension
Main articles: Surface tension
This
daisy is under the water level, which has risen gently and smoothly. Surface tension prevents the water from submerging the flower.
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 non-soluble surface such as
polythene; the water stays together as drops. Just as significantly, air trapped in surface disturbances forms bubbles, which sometimes last long enough to transfer gas molecules to the water.
Another surface tension effect is
capillary waves which are the surface ripples that form from around the impact of drops on water surfaces, and some times occur with strong subsurface currents flow to the water surface. The apparent elasticity caused by surface tension drives the waves.
Capillary action
Main articles: 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 surface tension tends to straighten the surface making the surface rise, and more water is pulled up through cohesion. The process is repeated as the water flows up the tube until there is enough water that gravity can counteract the adhesive force.
Solvation
High concentrations of dissolved
lime make the water of
Havasu Falls appear turquoise.
Water is a very strong
solvent, referred to as ''the universal
solvent'', dissolving many types of substances. Substances that will mix well and dissolve in water (e.g.
salts) are known as "
hydrophilic" (water-loving) substances, while those that do not mix well with water (e.g.
fats and oils), are known as "
hydrophobic" (water-fearing) substances. The ability of a substance to dissolve in water is determined by whether or not the substance can match or better the strong
attractive forces that water molecules generate between other water molecules. If a substance has properties that do not allow it to overcome these strong intermolecular forces, the molecules are "
pushed out" from the water, and do not dissolve.
Electrical conductivity
Pure water has a ''low''
electrical conductivity, but this increases significantly upon solvation of a small amount of ionic material water such as
hydrogen chloride. Thus the risks of
electrocution are much greater in water with the usual impurities not found in pure water. Any electrical properties observable in water are from 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. In pure water, sensitive equipment can detect a very slight electrical
conductivity of 0.055
µS/
cm at 25 °C. Water can also be
electrolyzed into oxygen and hydrogen gases but in the absence of dissolved ions this is a very slow process, as very little current is conducted. While electrons are the primary charge carriers in water (and metals), in ice (and some other electrolytes),
protons are the primary carriers (see
proton conductor).
Deuterated compounds of water
Hydrogen has three isotopes. The most common, making up more than 95% of water, has 1 proton and 0 neutrons. A second isotope,
deuterium (short form "D"), has 1 proton and 1 neutron. Deuterium, , is also known as
heavy water and is used in
nuclear reactors for storing nuclear wastes. The third isotope,
tritium, has 1 proton and 2 neutrons, and is
radioactive. does not exist in nature, as the creation of the rare molecule would result in its almost instantaneous decomposition. is stable, but differs from in being heavier and denser. It can also block alpha and beta rays. occurs naturally in water in very low concentrations. Consumption of pure isolated may affect biochemical processes: ingestion of large amounts impairs kidney and central nervous system function.
Water, ice, and vapor
Heat capacity and heat of vaporization
Main articles: Enthalpy of vaporization
Water has the second highest
specific heat capacity of any known chemical compound, after
ammonia, as well as a high
heat of vaporization (40.65 kJ mol
−1), both of which are a result of the extensive
hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's
climate by buffering large fluctuations in temperature.
Freezing point
A simple but environmentally important and unusual property of water is that its usual solid form,
ice, floats on its liquid form. This solid state is not as dense as liquid water because of the geometry of the hydrogen bonds which are formed only at lower temperatures. For almost all other substances the solid form has a greater
density than the liquid form. Fresh water at standard atmospheric pressure is most dense at 3.98 °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.
The water will freeze at 0 °C (32 °F, 273 K), however, it can be
supercooled in a fluid state down to its
crystal homogeneous nucleation at almost 231 K (−42 °C)
[7].
Ice also has a number of more exotic phases not commonly seen (go to the full article on
Ice).
Triple point
Main articles: Triple point
The
triple point of water (the single combination of pressure and temperature at which pure liquid water, ice, and water vapor can coexist in a stable equilibrium) is used to define the
kelvin, the SI unit of thermodynamic temperature. As a consequence, water's triple point temperature is a prescribed value rather than a measured quantity: 273.16 kelvins (0.01 °C) and a pressure of 611.73 pascals (approximately 0.0060373
atm).
This is approximately the combination that exists with 100% relative humidity at sea level and the freezing point of water.
Miscibility and condensation
Main articles: Humidity
Water is
miscible with many liquids, for example
ethanol in all proportions, forming a single homogeneous liquid. On the other hand water and most
oils are ''immiscible'' usually forming layers according to increasing density from the top.
Red line shows saturation
As a gas, water vapor is completely
miscible with air. On the other hand the maximum water vapor pressure that is thermodynamically stable with the liquid (or solid) at a given temperature is relatively low compared with total atmospheric pressure.
For example, if the vapor ''
partial pressure''
[8] is 2% of atmospheric pressure and the air is cooled from 25 °C, starting at about 22 °C water will start to condense, defining the
dew point, and creating
fog or
dew. The reverse process accounts for the fog ''burning off'' in the morning.
If one raises the humidity at room temperature, say by running a hot shower or a bath, and the temperature stays about the same, the vapor soon reaches the pressure for phase change, and condenses out as steam.
A gas in this context is referred to as ''saturated'' or 100% relative humidity, when the vapor pressure of water in the air is at the equilibrium with vapor pressure due to (liquid) water; water (or ice, if cool enough) will fail to lose mass through evaporation when exposed to saturated air. Because the amount of water vapor in air is small, ''relative humidity'', the ratio of the partial pressure due to the water vapor to the saturated partial vapor pressure, is much more useful.
Water vapor pressure above 100% relative humidity is called ''super-saturated'' and can occur if air is rapidly cooled, say by rising suddenly in an updraft.
[9]
Water on Earth
Origin and planetary effects
Much of the universe's water may be produced as a byproduct of
star formation.
When stars are born, their birth is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water we observe is quickly produced in this warm dense gas.
[10]
Solar distance and Earth gravity
The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth is vital to the existence of
life on Earth. The Earth is located in the
habitable zone of the
solar system; if it were slightly closer to or further from the
Sun (about 5%, or 8 million kilometers or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.
[11]
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 smaller, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in
polar ice caps (as on
Mars).
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''.
The state of water also depends on a planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity.
[1]
Tides
Main articles: Tide
'
Tides' are the cyclic rising and falling of
Earth's
ocean surface caused by the
tidal forces of the
Moon and the
Sun acting on the oceans. Tides cause changes in the depth of the marine and
estuarine water bodies and produce oscillating currents known as tidal streams.
The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the
effects of Earth rotation and the local
bathymetry.
The strip of seashore that is submerged at high tide and exposed at low tide, the
intertidal zone, is an important ecological product of ocean tides.
Water cycle
The
biosphere can be roughly divided into oceans, land, and atmosphere.
Water moves perpetually through each of these regions in the ''
water cycle'' consisting of following transfer processes:
★
evaporation from oceans and other water bodies into the air and
transpiration from land plants and animals into air.
★
precipitation, from water vapor condensing from the air and falling to earth or ocean.
★
runoff from the land usually reaching the
sea.
Most water vapor over the oceans returns to the oceans, but winds carry water vapor over land at the same rate as runoff into the sea, about 36
Tt per year. Over land, evaporation and transpiration contribute another 71 Tt per year.
Precipitation, at a rate of 107 Tt per year over land, has several forms: most commonly
rain,
snow, and
hail, with some contribution from
fog and
dew.
Condensed water in the air may also
refract sunlight to produce
rainbows.
Water runoff often collects over
watersheds flowing into rivers.
Some of this is diverted to
irrigation for agriculture. Rivers and seas offer opportunity for
travel and
commerce. Through
erosion, runoff shapes the environment creating river
valleys and
deltas which provide rich soil and level ground for the establishment of population centers.
Fresh water storage
Some runoff water is trapped for periods, for example in lakes.
At high altitude, during winter, and in the far north and south, snow collects in ice caps, snow pack and glaciers.
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.
This water storage is important, since clean, fresh water is essential to
human and other land-based life. In many parts of the world, it is in short supply.
Forms of water
Water takes many different forms on Earth:
water vapor and clouds in the sky;
seawater and rarely
icebergs in the ocean;
glaciers and rivers in the
mountains; and aquifers in the ground.
Water can dissolve many different substances, giving it different tastes and odours. In fact, humans and other animals have developed senses to be able to evaluate the
potability 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. The taste advertised in
spring water or
mineral water derives from the minerals dissolved in it, as pure H
2O is tasteless. As such,
purity in spring and mineral water refers to purity from
toxins,
pollutants, and
microbes.
Effects 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 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). Water is thus essential and central to these metabolic processes. Therefore, without water, these metabolic processes would cease to exist, leaving us to muse about what processes would be in its place, such as gas absorption, dust collection, etc.
Water is also central to photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. Hydrogen is combined with CO
2 (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 CO
2 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 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. Stomach acid (HCl) is useful to digestion. However, its corrosive effect on the esophagus during reflux can temporarily be neutralized by ingestion of a base such as
aluminum hydroxide to produce the neutral molecules water and the salt aluminum chloride. Human biochemistry that involves enzymes usually performs optimally around a biologically neutral pH of 7.4.
Aquatic life forms
Earth's waters are filled with life. Nearly all
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 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.
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 breathe air.
Effects on 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; the ancient society of the
Egyptians depended entirely upon the
Nile. Large
metropolises like
Rotterdam,
London,
Montreal,
Paris,
New York City,
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.
Health and pollution
Water fit for
human consumption is called
drinking water or
potable water. Water that is not potable can be made potable by distillation (heating it until it becomes water vapor, and then capturing the vapor without any of the impurities it leaves behind), or by other methods (chemical or heat treatment that kills bacteria). Sometimes the term
safe water is applied to potable water of a lower quality threshold (i.e., it is used effectively for nutrition in humans that have weak access to water cleaning processes, and does more good than harm). Water that is not fit for drinking but is not harmful for humans when used for swimming or bathing is called by various names other than potable or drinking water, and is sometimes called
safe water, or "safe for bathing". Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking. Its use is highly technical and is usually monitored by government regulations (typically 1 part per million (ppm) for drinking water, and 1-2 ppm of chlorine not yet reacted with impurities for bathing 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 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.
[12] 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 and over 1 billion without access to adequate sanitation. Poor water quality and bad sanitation are deadly; some 5 million deaths a year are caused by polluted drinking water. Water, however, is not a finite resource (like petroleum is), but rather re-circulated as potable water in precipitation in quantities many degrees of magnitude higher than human consumption. Therefore, it is the relatively small quantity of water in reserve in the earth (about 1% of our drinking
water supply, which is replenished in aquifers around every 1 to 10 years), that is a non-renewable resource, and it is, rather, the distribution of potable and irrigation water which is scarce, rather than the actual amount of it that exists on the earth. Water-poor countries use importation of goods as the primary method of importing water (to leave enough for local human consumption), since the manufacturing process uses around 10 to 100 times products' masses in water.
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 . The strain affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.
Human uses
For weighing
On
7 April 1795, the
gram was defined in
France to be equal to "the absolute weight of a volume of pure water equal to a cube of one hundredth of a meter, and to the temperature of the melting ice."
[13] For practical purposes though, a metallic reference standard was required, one thousand times more massive, the
kilogram. Work was therefore commissioned to determine precisely how massive one
liter of water was. In spite of the fact that the decreed definition of the gram specified water at 0 °C—a highly stable ''temperature'' point—the scientists chose to redefine the standard and to perform their measurements at the most stable ''density'' point: the temperature at which water reaches maximum density, which was measured at the time as 4 °C.
[14]
For drinking
A manual water
pump in China
About 70% of the fat free mass of the
human body is made of water. To function properly, the body requires between one and seven
liters 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. It is not clear how much water intake is needed by healthy people, though most experts agree that 8–10 glasses of water (approximately 2 liters) daily is the minimum to maintain proper hydration.
[15] For those who have healthy kidneys, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) it is 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.
[16] There are other myths such as the effect of water on weight loss and constipation that have been dispelled.
[17]
Original recommendation for water intake in 1945 by the
Food and Nutrition Board of the
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."
[18] The latest dietary reference intake report by the
United States National Research Council in general recommended (including food sources): 2.7 liters of water total for women and 3.7 liters for men.
[19] Specifically,
pregnant and
breastfeeding women need additional fluids to stay hydrated. According to the
Institute of Medicine—who recommend that, on average, women consume 2.2 litres and men 3.0 litres—this is recommended to be 2.4 litres (approx. 9 cups) for pregnant women and 3 litres (approx. 12.5 cups) for breastfeeding women since an especially large amount of fluid is lost during nursing.
[20] Also noted is that normally, about 20 percent 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 that does not contain too many impurities. Common impurities include metal salts and/or harmful
bacteria, such as ''
Vibrio''. Some
solutes are acceptable and even desirable for taste enhancement and to provide needed
electrolytes.
The single largest freshwater resource suitable for drinking is
Lake Baikal in Siberia, which has a very low
salt and
calcium content and is very clean.
As a solvent
Dissolving (or
suspending) is used to wash everyday items such as the human body, clothes, floors, cars, food, and pets.
As a thermal transfer agent
Boiling,
steaming, and
simmering are popular
cooking methods that often require immersing food in water or its gaseous state, steam. Water is also used in industrial contexts as a
coolant, and in almost all power-stations as a coolant and to drive steam
turbines to generate electricity. In the nuclear industry, water can also be used as a
neutron moderator.
Recreation
Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include
swimming,
waterskiing,
boating,
fishing, and
diving. In addition, some sports, like
ice hockey and
ice skating, are played on ice.
Lakesides and beaches are popular places for people to go to relax and enjoy recreation. Many find the sound of flowing water to be calming, too. Some keep fish and other life in
water tanks or
ponds for show, fun, and companionship. Humans also use water for snow sports i.e.
skiing or
snowboarding, which requires the water to be frozen.
People may also use water for
play fighting such as with
snowballs,
water guns or
water balloons.
They may also make fountains and use water in their public or private decorations.
Industrial applications
Pressurized water is used in
water blasting and
water jet cutters. Also, very high pressure water guns are used for precise cutting. It works very well, is relatively safe, and is not harmful to the environment.
Food processing
Water plays many critical roles within the field of
food science. It is important for a food scientist to understand the roles that water plays within food processing to ensure the success of their products.
Solutes such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water is affected by solutes. One
mole of sucrose (sugar) raises the boiling point of water by 0.52 °C, and one mole of salt raises the boiling point by 1.04 °C while lowering the freezing point of water in a similar way.
[21] Solutes in water also affect water activity which affects many chemical reactions and the growth of microbes in food.
[22] Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water.
Solutes in water lower water activity. This is important to know because most bacterial growth ceases at low levels of water activity.
22 Not only does microbial growth affect the safety of food but also the preservation and shelf life of food.
Water hardness is also a critical factor in food processing. It can dramatically affect the quality of a product as well as playing a role in sanitation. Water hardness is classified based on the amounts of removable calcium carbonate salt it contains per gallon. Water hardness is measured in grains; 0.064 g calcium carbonate is equivalent to one grain of hardness.
Water is classified as soft if it contains 1 to 4 grains, medium if it contains 5 to 10 grains and hard if it contains 11 to 20 grains.
The hardness of water may be altered or treated by using a chemical ion exchange system. The hardness of water also affects its pH balance which plays a critical role in food processing. For example, hard water prevents successful production of clear beverages. Water hardness also affects sanitation; with increasing hardness, there is a loss of effectiveness for its use as a sanitizer.
Power generation
Hydroelectricity is electricity obtained from
hydropower. Hydroelectric power comes from water driving a water turbine connected to a generator. Hydroelectricity is a low-cost, non-polluting, renewable energy source.
Politics
Because of
overpopulation,
mass consumption, misuse, 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.
[23] 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 from easily preventable water-related diseases; often this means lack of
sewage disposal; see
toilet. The
United Nations Development Programme sums up world water distribution in the 2006 development report: "While one part of the world sustains a designer bottled-water market that generates no tangible health benefits, another part suffers acute public health risks because people have to drink water from drains or from lakes and rivers."
[24] 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.
OECD countries
With nearly 2,000
cubic metres (70,000 ft
3) of water per person per year , the
United States leads the world in water consumption per capita. In the Organization for Economic Co-operation and Development (
OECD) countries, the U.S. is first for water consumption, then
Canada with 1,600 cubic meters (56,000 ft
3) 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).
[25][26]
United States
Ninety-five percent of the United States' fresh water is underground. One crucial source is a huge underground reservoir, the 1,300-kilometer (800 mi)
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 meters (420 billion ft
3) per 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.
[27]
Mexico
In
Mexico City, an estimated 40% of the city's water is lost through leaky pipes built at the turn of the 20th century.
[28]
Middle East
The
Middle East region has only 1% of the world's available fresh water, which is shared among 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.
[29] According to a report by the
Arab League, two-thirds of Arab countries have less than 1,000 cubic meters (35,000 ft
3) of water per person per year available, which is considered the limit.
[30]
Jordan, for example, has little water, and
dams in other countries have reduced its available water sources over the years. The 1994
Israel-Jordan Treaty of Peace stated that Israel would give 50 million cubic meters of water (1.7 billion ft
3) 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.
[31] 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 conflictive 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.
[32]
Both
Israel and Jordan rely on the
Jordan River, but Israel controls it, as well as 90% 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 practice 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.
[33] Israelis in the
West Bank use four times as much water as their Palestinian neighbors.
[34] According to the
World Bank, 90% of the
West Bank's water is used by Israelis.
32 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 (27 billion ft
3) of water per year to Israel, which represents a third of its annual consumption. The Golan's water goes to the
Sea of Galilee—Israel's largest reserve—which is then redistributed throughout the country by the
National Water Carrier. 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 the construction of desalination plants.
[34]
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.
[36] 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).
Asia
Three Gorges Dam, receiving, upstream side,
26 July,
2004
In
Asia,
Cambodia and
Vietnam 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 the world's largest
dam, 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, which is causing subsoil streams flowing into the Ganges river to dry up. Downstream, India controls the flow to
Bangladesh with the
Farakka Barrage, 10 kilometers (6 mi) on the Indian side of the border. Until the late 1990s, India used the barrage to divert the river to
Calcutta to keep the city's port from drying up during the dry season. This denied Bangladeshi farmers water and
silt, and it 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 problem, with high levels of
arsenic and untreated sewage in the river water.
[37]
South America
The
Guaraní Aquifer, located between the
Mercosur countries of
Argentina,
Brazil,
Bolivia and
Paraguay, with a volume of about 40,000 km³, is an important source of fresh potable water for all four countries.
Privatization
Privatization of water companies has been contested on several occasions because of poor water quality, increasing prices, and ethical concerns. In
Bolivia for example, the proposed privatization of water companies by the
IMF was 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 because of similar protests in
Buenos Aires,
Santa Fe, and
Córdoba, Argentina. Consumers took to the streets to protest water rate hikes of as much as 500% 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''.
[38]
South Africa also made moves to privatize water, provoking an outbreak of cholera killing 200.
[39]
In 1997, World Bank consultants assisted the Philippine government in the privatization of the city of Manila's Metropolitan Waterworks and Sewerage Systems (MWSS). By 2003, water price increases registered at 81% in the east zone of the Philippines and 36% in the west region. As services became more expensive and inefficient under privatization, there was reduced access to water for poor households. In October 2003, the Freedom from Debt Coalition reported that the diminished access to clean water resulted in an outbreak of cholera and other gastro-intestinal diseases.
[40]
Regulation
A water-carrier in India, circa ~1882. In many places where running water is not available, water has to be transported by people.
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 by 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. Like other types of pollution, this does not enter standard accounting of market costs, being conceived as
externalities for which the market cannot account. Thus other people pay the price of 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.
Religion, philosophy, and literature
Water is considered a purifier in most religions. Major faiths that incorporate ritual washing (
ablution) include
Hinduism,
Christianity,
Islam,
Judaism, and
Shinto. Water
baptism is a central
sacrament of Christianity; it is also a part of the practice of other religions, including Judaism (''
mikvah'') and
Sikhism (''
Amrit Sanskar''). 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 in
most cases after completing washing certain parts of the body using clean water (''
wudu''). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual of ''
misogi''). 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).
Some faiths use water especially prepared for religious purposes (
holy water in some Christian denominations, ''
Amrit'' in Sikhism and Hinduism). Many religions also consider particular sources or bodies of water to be sacred or at least auspicious; examples include
Lourdes in
Roman Catholicism, the
Zamzam Well in Islam and the River
Ganges (among many others) in Hinduism. In Neo-Paganism water is often combined with salt in the first steps of a ritual, to act as a purifier of worshippers and the altar, symbolising both cleansing tears and the ocean.
Water is often believed to have spiritual powers. In
Celtic mythology,
Sulis is the local
goddess of thermal springs; in
Hinduism, the
Ganges 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. In
Islam, not only does water give life, but every life is itself made of water: "We made from water every living thing".
[41]
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.
Water also plays an important role in
literature as a
symbol of
purification. Examples include the critical importance of a
river in ''
As I Lay Dying'' by
William Faulkner and the
drowning of Ophelia in ''
Hamlet''.
See also
: ''Main lists:
List of water related topics and
List by water type''
References
1. http://pubs.acs.org/cgi-bin/abstract.cgi/bichaw/1997/36/i43/abs/bi971323j.html
2.
Water Vapor in the Climate System, Special Report, [AGU], December 1995 (linked 4/2007). Vital Water UNEP.
3. [http://www.time.com/time/health/article/0,8599,1642811,00.html Water Found on Distant Planet July 12, 2007 By LAURA BLUE TIME
4. Water Found in Extrasolar Planet's Atmosphere - Space.com
5. Why is water blue?
6. Physical Forces Organizing Biomolecules (PDF)
7. P. G. Debenedetti, P. G., and Stanley, H. E.; "Supercooled and Glassy Water", Physics Today 56 (6), p. 40–46 (2003).
8.
The pressure due to water vapor in the air is called the 'partial pressure'(Dalton's law) and it is directly proportional to concentration of water molecules in air (Boyle's law).
9.
''Adiabatic cooling'' resulting from the ideal gas law.
10. Gary Melnick, Harvard-Smithsonian Center for Astrophysics and David Neufeld, Johns Hopkins University quoted in:
Discover of Water Vapor Near Orion Nebula Suggests Possible Origin of H20 in Solar System [sic]
Space Cloud Holds Enough Water to Fill Earth's Oceans 1 Million Times
Water, Water Everywhere: Radio telescope finds water is common in universe .
(linked 4/2007)
11. J. C. I. Dooge. "Integrated Management of Water Resources". in E. Ehlers, T. Krafft. (eds.) ''Understanding the Earth System: compartments, processes, and interactions. Springer, '2001', p. 116. More references are at the end of the article "Habitable Zone" at The Encyclopedia of Astrobiology, Astronomy and Spaceflight.
12. G8 "Action plan" decided upon at the 2003 Evian summit
13. ''Decree relating to the weights and measurements''
14. Citation: ''L'Histoire Du Mètre, La Détermination De L'Unité De Poids'', link to Web site here.
15. Healthy Water Living
16. "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 × 8"? by Heinz Valdin, Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire
17. Drinking Water - How Much?, Factsmart.org web site and references within
18. Food and Nutrition Board, National Academy of Sciences. Recommended Dietary Allowances, revised 1945. National Research Council, Reprint and Circular Series, No. 122, 1945 (Aug), p. 3-18.
19. Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate, Food and Nutrition Board
20. http://www.mayoclinic.com/health/water/NU00283
21. Vaclacik and Christian, 2003
22. DeMan, 1999
23. A Chronology of Water-Related Conflicts
24. UNDP Human Development Report 2006 United Nations Development Programme, 2006.
25. Water consumption indicator in the OECD countries
26. Golf 'is water hazard'
27. Ogallala aquifer - Water hot spots
28. Mexico City - Water hot spots
29. Water shortages 'foster terrorism'
30. "Major aspects of scarce water resources management with reference to the Arab countries", Arab League report published for the International Conference on water gestion and water politics in arid zones, in Amman, Jordan, December 1-3, 1999. Quoted by French journalist Christian Chesnot in Drought in the Middle East - French original version freely available here.
31. See 1994 Israel-Jordan Treaty of Peace, annex II, article II, first paragraph
32. See Christian Chesnot in Drought in the Middle East - French original version freely available here.
33. Analysis: Middle East water wars, by Abel Darwish
34. Israel - water hot spots
35. Israel - water hot spots
36. Turkey - water hot spots
37. Ganges river - water hot spots
38. Bolivia's water wars coming to end under Morales
39. Water privatisation: ask the experts
40. Rights Education Empowers People in the Philippines
41. Sura of Al-Anbiya 21:30
Further reading
★
Principles of Food Chemistry 3rd Edition, John M. DeMan, , , , 1999,
★
Essentials of Food Science 2nd Edition, Vickie A. Vaclavik and Elizabeth W. Christian, , , , 2003,
★ OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? ''TRENDS in Biotechnology'' 23(4): 163, 2005
★ Franks, F (Ed), Water, A comprehensive treatise, Plenum Press, New York, 1972-1982
★
Property of Water and Water Steam w Thermodynamic Surface
★ PH Gleick and associates, The World's Water: The Biennial Report on Freshwater Resources. Island Press, Washington, D.C. (published every two years, beginning in 1998.)
★ Marks, William E., The Holy Order of Water: Healing Earth's Waters and Ourselves. Bell Pond Books ( a div. of Steiner Books), Great Barrington, MA, November 2001 [ISBN 0-88010-483-X]
★ Debenedetti, P. G., and Stanley, H. E.; "Supercooled and Glassy Water", ''Physics Today'' '56' (6), p. 40–46 (2003).
Downloadable PDF (1.9 MB)
Water as a natural resource
★
The World's Water: The Biennial Report on Freshwater Resources, , Peter H., Gleick, Island Press, , (November 10, 2006)| ISBN-13: 9781597261050]
★
Last Oasis: Facing Water Scarcity, , Sandra, Postel, Norton Press, 1997, second edition,
★
Water Rights: Scarce Resource Allocation, Bureaucracy, and the Environment, Anderson, , , , 1991,
★
Water: The Fate of Our Most Precious Resource, Marq de Villiers, , , , 2003, revised edition,
★
Water Wars: Drought, Flood, Folly and the Politics of Thirst, Diane Raines Ward, , , , 2002,
★
Water and Power: The Politics of a Scarce Resource in the Jordan River Basin, Miriam R. Lowi, , , , 1995, (Cambridge Middle East Library)
★
Rivers of Empire: Water, Aridity, and the Growth of the American West, , Donald, Worster, , 1992,
★
Cadillac Desert: The American West and Its Disappearing Water, , Marc, Reisner, , 1993,
★
Blue Gold: The Fight to Stop the Corporate Theft of the World's Water, Maude Barlow, Tony Clarke, , , , 2003,
★
Water Wars: Privatization, Pollution, and Profit, Vandana Shiva, , , , 2002, ISBN 0-7453-1837-1
★
Troubled Water: Saints, Sinners, Truth And Lies About The Global Water Crisis, Anita Roddick, et al, , , , 2004,
★
The Holy Order of Water: Healing Earths Waters and Ourselves, William E. Marks, , , , 2001,
External links
★
American Water Resources Association
★
WaterAid - Charity dedicated to the provision of clean water, sanitation and hygiene education
★
Properties Water and Water Steam
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