Water - the Basics         Water and the universe
The Universe as we know it began with the Big Bang which scientists estimate to have occurred roughly 15 billion years ago. There was no water in the universe at his time, and in fact no atoms existed, just a huge fiery furnace that blazed at over 100 billion degrees centigrade.

However out of this intense heat, atoms began to be formed. Hydrogen, the smallest, lightest and most important of all the atoms, came into being as electrons formed around a nucleus of protons and neutrons to form first atom. These hydrogen atoms, and later helium, combined to create a great gas cloud, which invaded and materialised the great void, creating matter. As gravity began to exert is inexorable pull, solidifying this gaseous clod into solid matter, planets began to be formed, among them our own solar system.

Water on the Planets

Within our own solar system, there are a few planets on which water once existed, leaving to possibility of life existing, or having existed, at one time. Water is the essential factor in creating the environment for life, and therefore scientists have sought to discover water on the surrounding planets in our own solar system.

The Moon

In 1998, the space probe Lunar Prospector revealed the existence of large amounts of ice on the Moon. Concentrated mainly around the lunar poles (in particular the southern pole), this ice appears to be a mixture of water and ìmoon dustî (regolith). This exciting discovery means that projects for establishing human settlements on the Moon, once considered science fiction stories, may in fact be possible. Projects are envisaged which include establishing base camps for research and exploration, from which probes could be launched to other planets, in particular Mars, to search for traces proving whether or not any life forms exist now, or did in the past, on the « red planet ».

Jupiter’s satellites

Europa

The surface of Jupiter’s satellite moon Europa is covered with ice. The enormous gravitational pull from Jupiter has caused this ice to buckle and crack. Astronomers watching this ice over time have observed that the cracks seem to fuse back together sometimes. Does this observed phenomenon imply the presence of water beneath Europa’s surface? One hypothesis is that there might well be a deep ocean hidden below the surface of this moon, harbouring primitive life forms. The discovery of geysers of ice on Europa’s surface in 1996 by the Galileo space probe has strengthened this hypothesis. NASA plans to send another probe to analyse the chemical composition of any water found; this could confirm whether or not any organic chemicals exist on Europa.

Ganymede

A layer of ice 900 kilometres thick (over 550 mi) covers Ganymede, one of the largest planetary satellites in our solar system. Strange parallel ridges resembling scratches or cracks criss-cross the surface of this ice. A hypothesis has been put forward which suggests that there is water beneath the ice that expands as it freezes, causing the surface to buckle and warp.

Callisto

Enormous quantities of ice push upwards from the depths of Callisto, and large craters, formed by the impact of huge meteorites, dot the surface of this satellite.

Saturn’s satellites

Enceladus

Enceladus resembles an enormous ice cube orbiting around Saturn. The temperature here remains fixed at _220°C (_364°F).

Titan

Titan’s surface appears to be composed mostly of ice. A kind of "snow" falls here regularly, the result of the condensation of water vapour from the satellite’s upper atmosphere. In 2004, Titan will be visited by the Huygens space probe searching for evidence of pre-biotic molecules (molecules that are precursors to living entities).

Mars

The surface of Mars, the red planet, is covered with lines once thought to be canals. In a distant past, the atmosphere of Mars was extremely dense, and the temperature and atmospheric pressure would have permitted water to remain liquid. Are these traces the remains of ocean beds, the trails of glaciers or the imprint of rivers that have disappeared? Geologists have suggested that these marks may have been caused by water erosion. But no one can explain why the water has now disappeared. Planetologists speculate that the axial rotation of Mars has switched back and forth several times, resulting in a series of extreme climate changes that provoked the disappearance of the water from the surface. We know that some of this water is stocked in the form of ice at each pole. It is presumed that the rest evaporated into space; some scientists think that the remainder is buried in the frozen depths of the planet itself. If these hypotheses are correct, then life on Mars is perhaps in hibernation.

The Earth

The Earth seems to be the only planet in this solar system with water present in all three of it physical states, namely, liquid, solid and gaseous. In the present state of knowledge, the Earth appears to be the only planet with all the necessary conditions for the appearance of life, at least as we know it. 

Water in one form or another may be found throughout the known universe, and since it appears that life is possible only when water is present, scientists are always very interested each time the discovery of water can be confirmed on one of the other planets in the solar system.

Water cycle
Water is the most widespread substance on the world surface, and exists in three states: liquid, solid and invisible vapour. It forms oceans, seas, lakes, rivers and underground waters, found in the top layers of the Earth’s crust and soil cover. In its solid form, it exists as snow and ice in polar and alpine regions, and as a gas it exists in the air as water vapour and clouds. 

This water is in a constant state of flux between its different forms, and hence very difficult to measure. Current estimates suggest that the Earth contains about 1386 million cubic kilometres of water, although 97.5% of this is salt water. The majority of the remaining 2.5% of fresh water, about 68.7%, is found in the permanent snow cover in the Arctic and Antarctic regions. About 29.9% exists as fresh ground waters, yet of this only 0.26% is concentrated in lakes, reservoirs and river systems, and therefore easily available for humans to use. 

These values only represent long-term averages of the amount of water in various states. In fact this water is constantly varying, and the nature and volume of water stored in the hydrosphere will alter due to the process known as the Hydrological, or Water, Cycle. The Water Cycle is a fairly familiar concept to most of us who have sat through geography classes at school. The basic principles of the cycle are essentially the same:

1) Water evaporates from the ocean and condenses into precipitation which falls on the continents

2) The water then either runs into streams and lakes, or filters down through the earth before ending up back in the sea where the process begin again.

However, this simple model is slightly more complicated in reality, particularly as in certain areas one or two storms may provide a year’s worth of rainfall in a few hours, and rain may fall in unequal quantities over the Earth’s surface.

Link 
International Glossary of Hydrology
http://www.cig.ensmp.fr/~hubert/glu/aglo.htm

This glossary is a contribution to the International Hydrological Programme of UNESCO by the French National Hydrology Committee. Available in 12 languages.

The Brief History of the Water Cycle

During history, different people have struggled to understand the changing amount of water on the world.

The principal mystery of the water cycle was why the sea level did not rise despite the continuous inflow from the rivers. To solve this, it would have been necessary to estimate the large quantity of sea water evaporated by the heat of the sun. However, that was not possible since it was assumed that the seas covered only a limited surface area in a flat and disc-shaped world. This notion, inherited from Ptolemy (90-168 AD), faded out in the West, especially under the influence of Copernicus (1473-1543) and Galileo (1564-1642).The Greeks therefore described the water cycle backwards, arguing that since the level of the seas remained constant despite all the rivers flowing into it, the water must penetrate the earth’s depths and feed the underground springs. Evaporation and Precipitation were ignored. Egypt presented another paradox for the ancient world. The Nile flooded at the height of the dry season and those living along its banks did not know where the source of the river was. That discovery was only made in the late nineteenth century by Europeans. In ancient Egypt the lower castes thought that the Nile was just a branch of the Mediterranean and believed that the sea water rose in the river, in much the same way as in a bay in Brittany. The educated classes, however, measured the floods with the first scales to be set in the bed of the river, the famous nilometers. 

Outside Europe, however, the Chinese had understood the water cycle 500 years before the birth of Christ, and in India, Kautilya, a minister of the Maurya dynasty (321-185 BC), had rain measured in pails placed in front of rural stores. In terms of public services, the first flood-warning system, set up by the Chinese in 1574 on the Yellow River, used horseback riders who travelled faster than the water. The Koreans started taking regular, systematic rainfall measurements in 1441 and have continued doing so ever since. In other ancient civilisations such as ancient Egypt, Greece, Palestine and India, attempts were made to record the level of water, often as a means of charging tax. This practice also occurred in China and Korea, especially during and after the 15th century. 

Leonardo da Vinci and the French scientist Bernard Palissy were two of the most brilliant theorists of primitive hydrology, and the concept of a water cycle began to take shape during this period. William Shakespeare in A Midsummer Night’s Dream, Act 2, Scene 1 has a fairly accurate notion of the process:

Therefore the winds, piping to us in vain, 
As in revenge have suck’d up from the sea 
Contagious fogs; which, falling on the land, 
Have every pelting river made so proud 
That they have overbourne their continents.

Hydrology only became a science in the 17th century with the advent of accurate measurements and the establishment of general hydrological assessments, which led to the formulation of the general principle that nothing is created, noting destroyed. The scientist Pierre Perrault undertook the first hydrological record-keeping in the Seine River Basin. In his treatise The Origin of Fountains (1674) he demonstrated that springs and therefore rivers are fed by rain. In the 1690’s Edmund Halley, primarily known as an astronomer and as the discoverer of the comet that bears his name, elaborated a method to measure evaporation, and hence demonstrated that evaporation was the reason for the deficit in water discharge from rivers that had been previous discovered.

Links

International Hydrological Program
http://www.unesco.org/water/ihp/index.shtml

National Water Research Institute
http://www.inre.ca/

Comprehensive Assessment of the Freshwater Resources of the World
http://www.un.org/dpcs/dsd/freshwat.htm
Water science for Schools/US Geological Survey
http://ga.water.usgs.gov/edu/
Global Hydrology and Climate Center
http://www.ghcc.msfc.nasa.gov

Chemical properties
In order to understand the true significance of this magical substance, we ought to start with its chemical structure. Most of you probably know the basic chemical formula of water, H2O. This means that one atom of oxygen is bound to two atoms of hydrogen. 

One of the crucial facts about water is its charge. Due to the fact that hydrogen molecules are attached to one side of the oxygen atom, the water molecule has a positive charge on one side, and a negative on the other, making water a ‘sticky’ substance. This sounds strange – how can water be ‘sticky’? But if water didn’t have this charge, water molecules would not attract one another, there would be no drops of water, no rain, as the molecules would simply spread out and disperse. 

In addition, water is pH 7, which is known as neutral; it is neither acid nor alkali.

Water is also called the universal solvent as it dissolves more substances than any other liquid. That means that water carried with it, when it moves through the ground or our bodies, valuable minerals, chemicals and nutrients.

Physical properties
Water exists in three states – gas (steam), liquid (water) and solid (ice). It is unique among natural substances in that it exists in all three different states at temperatures found on the earth’s surface. The earth’s water is constantly moving between these three states, and the state of the earth’s water is a pressing concern, particularly in relation to global warming.

Water freezes at 32 Fahrenheit, and boils at 212 Fahrenheit. However, these values change according to the level of atmospheric pressure and the level of altitude. At the top of a Mount Everest, water boils much more easily. Water’s freezing and boiling points are the base points with which temperature is measured according to the Celsius scale. 0 on the Celsius scale is water’s freezing point, and 100 is its boiling point.

Water is unusual in that its solid form, ice, is less dense than its liquid form. That is why ice floats, and explains why icebergs float on the ocean.

Water has a high specific heat index, which means that it requires a lot of energy to heat water up, as anyone who has used a kettle will know. This makes water hugely important to industry, as well as in your car radiator, since it works as a coolant. We also see this phenomenon is our climate; near the oceans the weather is more equitable, since the temperature change in the climate is restrained by the presence of water, which takes longer to cool down and heat up.

Water has a high surface tension, due to its sticky quality. It forms droplets, rather that a thin layer of molecules. Surface tension is responsible for capillary action, which allows water to move through the roots of plants and through the tiny blood vessels in our bodies.

Water and life
Have a look at the person next to you. What percentage of their body is water do you think? They look solid enough, but there is bound to be some water in the stomach, and probably some around the rest of the body, so maybe you are thinking around 30 percent. Would it surprise you to know that in fact the answer is nearer to 60 %?

Water is essential to all living things. The composition of a six-week-old foetus includes 97% water. This volume of water diminishes progressively between birth and death. In one sense, aging might be considered as a continuous process of drying out.

The actual percentage of water in the human body is related to the shape of each individual. The water content of individuals of the same height is inversely proportionate to the amount of fatty tissue present in the body. Therefore a very slender individual may contain over 70% water, while a more fleshy person will contain only 30%. The various organs in the body contain different amounts of water as well:

Brain - 80%-90%
Lungs - 80%
Bones and cartilage - 20%

Water does simply slosh around the body, but exists in two separate forms. Most body water is intracellular liquid, which constitutes up to 60% of total liquid mass of an organism. The rest, labelled extracellular liquid, is found outside the cells. A large amount of liquid is found in the circulatory system, obviously in the blood, but also in the lymph. All of the cells, organs and tissues in the body are bathed in extracellular liquid. This is what is meant by internal water.

Water requirements

Since water represents on average about 60% of an adult’s total mass, one of the body’s most important tasks is to ensure that this water is replenished on a continuous basis. An individual who lives in a temperate climate, for example somewhere in Western Europe, and exerts no great physical effort, must absorb between 1 and 1.5 litres (1-1.5 qts) of water per day in order to survive. This minimum quantity increases to 3 litres (3 qts) or more in hot climates, such as desert areas or the tropics, and also increased following physical activity. In hot, dry desert regions, it is practically impossible to survive without water for more than two days, unless you are a camel.

Thirst

It a hot day, you’ve just been running around with some friends, and your mouth is parched – what going on? This sensation is what happens when our body is sending our brain messages in the form of hormones, which in turn sets off the thirst alarm, telling us to get a drink. In fact this mechanism is an emergency precaution, and it is never a good idea to wait to drink until thirst has set in, which is why people should drink more water than their thirst seems to tell them they need.

Absorption and elimination of water

A normal adult weighing roughly 70 kilos (150 lbs) at rest in a temperate climate loses from 2 to 2.5 litres (2-2.5 qts) of water per day, which must be replaced through food and drink in order to maintain an equilibrium. Dehydration can be fatal to human beings, and a loss of 20% of the total volume of body water means that the organism will die. However, drinking liquids is not the only way for the body to replenish water loss. Eating is also crucial to this process, and when we eat, we absorb on average one litre (1 qt) of water per day. In addition, the breakdown of food during digestion also provides endogenous, or internally derived, water to the body at the rate of 300 to 400 ml (10 to 13 oz) per day. However, this endogenous water does not allow a human to survive for any length of time, but for certain animal species living in extremely harsh habitats, such as the hot deserts, it is the only water available. 

This table below illustrates the percentage of water content in various different foodstuffs.

Table of percentage of water in certain foods

1 litre of milk/1qt milk - 91%
1 litre of beer/1 qt beer, 3.6% alcohol - 91%

Mushrooms - 90%
1 litre of wine/ 1 qt wine, 10% alcohol - 87%
Cherries - 83% 
Potatoes - 78%
Yoghurt - 75%
Fresh fish - 70%
Red meat - 60%
Soft cheese - 50%
Fresh bread - 35%
Crackers - 6%
Hazelnuts - 5%
Chocolate - 2%
Oil - 0%
The kidneys are the most crucial organ with regards to bodies water requirements, and are responsible for managing and maintaining a balance in body fluids. The kidneys are composed of millions of small juxtaposed tubes called nephrons whose walls act as filters. In the filtration process, also called dialysis, the kidneys separate the mineral salts and water necessary for the body and return them to the bloodstream; they reject the surplus of other substances and eliminate them in the form of urine (such as excess vitamins which cannot stocked in the body; this is why it is pointless to take more vitamins than the body can absorb). The kidneys help the body to regulate levels of other substances as well, such as uric acid, cholesterol and sugar.

Link

Water science for Schools/US Geological Survey

http://ga.water.usgs.gov/edu/