issue 207 - May 1990
the magic of water
Where did water come from?
Millennia ago, heat in the interior of the young earth drove oxygen and hydrogen atoms out of combination inside the rocks in which they were contained. The newly formed molecules came to the surface in streams of lava and were then released as water vapour. Great clouds formed that rained once the earth had cooled and covered it with seas. So what are now oceans were once our rocks. These oceans cover 71 per cent of the earth's surface and have an average depth of six kilometres.
Water has a very peculiar property: it is liquid at room temperature. So small a molecule, according to the organic chemists, ought to be a gas, like ammonia or methane. But water molecules find themselves strapped together by networks of hydrogen bonds, linking molecule to molecule by the power of their electronic attraction. This forces them to cluster together as a liquid instead of moving around independently as a gas.
The curious character of ice
Another chemical oddity is that water, unlike any other liquid that freezes, becomes less dense as it solidifies. Here again, the hydrogen bonds play tricks, holding the molecules of water apart as well as together, gripping firmly but at arm's length. This means that ice floats on water, with the ice forming or drifting on the surface of the drink, the sea or the lake. If ice sank and rivers froze upwards, aquatic life could not survive the harshness of winter in any cold climate.
An ecological miracle
The chemists are equally amazed by water's capacity to absorb heat. According to its molecular size, water ought to boil at -93°C. This would rather cramp its use for cooking and heating. Water's storage of heat has extraordinary ecological consequences. The oceans act as vast solar-energy reservoirs: every 90 minutes the Gulf Stream releases to the air as much energy as humans worldwide produce in a year through burning coal. As water masses move towards the poles, the energy they liberate keeps the climate temperate, creating an environment in which life can flourish.
Water on the brain
Around 70 per cent of the human body is made up of water. Brain and muscle tissues are water-richest, bone and fat water-poorest. Water also performs the role of solvent and conductor essential to the metabolic performance of the human being. Every day our bodies turn over 2.5 litres of water, losing most of this by respiration, perspiration, and excretion, and replacing the shortfall by the combustion of food and drink. Without the body's natural cooling process - in which water is essential - this combustion would cause a rise in body temperature of 26°C.
The global bucket
The vast majority of the water on earth - over 97 per cent - is contained in the oceans. With its high mineral content this is no use for sustaining earth-bound plant or animal life. Most of the freshwater is locked up in the icecaps and glaciers, leaving only 0.6 per cent in lakes, rivers, and under the ground as an accessible resource vital to human activity. Nevertheless there is plenty to go round: 3,000 cubic metres per person per year at present. But pressures from expanding population, irrigated agriculture and thirsty industrial processes are growing.
The hydrological cycle
Every schoolchild is taught the wonders of the rain-and-shine system whereby water is endlessly recycled through the atmosphere from sea to land, fuelling plant and animal fertility in the process. Each year the sun's energy draws 500,000 cubic kilometres of seawater into the air. Around one-fifth of this falls back on land as rain, setting off down rivers and streams towards the sea to repeat the cycle. The amount of water in the cycle is constant and cannot be changed.
The rain in Spain...
But this constant amount of water in the global bucket pours on some countries and continents much more than others - it favours those who live in the green and pleasant lands of the temperate zones. Many parts of Asia and Africa face grave water shortages. Paradoxically it is also these regions which are most prone to flooding as run-off turns dry seasonal rivers into raging torrents, causing immense damage. Because of population growth, global supplies per head of this finite resource are dropping, and the sharpest drops are in already water-short countries.
The matrix of life
We can live without oil if we have to; we cannot survive a day on earth without water. Its ready supply is too easily taken for granted, especially in temperate parts of the world. As pressure increases on our supply - pressure from people, industrial processes, pollutants - water is in grave danger of becoming just another commodity in the market place, and supplies are dominated by the rich and powerful. In the traditional world, in religion and even in municipal engineering, water has always been seen as a common resource, indivisible as air. Equity demands that it remains so.
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