There are about 1,360 million cubic kilometres of water on the earth. If all the water, on the planet; from oceans, lakes, rivers, the atmosphere, underground aquifers and what is locked up in glaciers and snow, were all released at once the earth’s surface could be flooded to an overall depth of some three kilometres.
More than 97 per cent of this water is in the oceans. The rest-about 37 million cubic kilometres-is fresh water but most of that is of little use since it is locked in icecaps and glaciers. Current estimates are that about 8 million cubic kilometres are stored in relatively inaccessible ground water and about 0.126 million cubic kilometres are contained in lakes and streams.
Like coal, oil, iron or soil, water is a natural resource. But there are many ways in which water differs from other natural resources. First, it moves. Second, its total quantity on the earth is fixed and can be neither increased nor decreased. Thirdly, water is essential for human survival.
The human being’s biological need for water is modest. A dozen or so cupfuls a day are all that are required for survival. Even so, there are many areas of the earth where even this requirement is difficult to meet. Rainfall in many desert regions is limited to a few millimetres a year, and this often falls at unpredictable times during the space of a few isolated days. Survival in these regions is impossible unless water is imported.
Biological survival, however, is not the issue in today’s water-stressed world. Water is required for household needs, for industry and agriculture. Household needs-drinking, washing and cooking-could be adequately met everywhere in the world by less than 100 litres per person per day, roughly the amount used for an average shower. Of this, only one litre a day is required for drinking. A hundred litres a day is the equivalent of about 35 cubic metres per person a year. If every man, woman and child on the planet were provided with 100 litres of domestic water a day, the water bill for a population of 5 billion people would be 180,000 billion litres a year; or 180 cubic kilometres. In theory, the Amazon river alone with an annual flow of nearly 6000 cubic kilometres could supply the domestic water needs of a world population more than 30 times as large as it is now.
A supply of unpolluted drinking water and the sanitary disposal of human wastes are fundamental to health. Water pollution moves through shared rivers, lakes and seas. An estimated 60 million people died of diarrhoea diseases due to unsafe drinking water and malnutrition, most of the victims were children.
Irrigation is by far the biggest use of water and also the most rapidly expanding. Plants use large quantities of water during their growth. Under dry conditions, it takes about 1000 cubic metres of water to produce one tonne of plant growth. The amount of water used for irrigation has increased 10 times this century and elaborate plans are still being made to extend irrigation to more and more areas. The basic addition is simple: 565 cubic kilometres for domestic, industrial, cooling and livestock use, plus 3,300 cubic kilometres for irrigation. As near as makes little difference, the answer is 4000 cubic kilometres a year, equivalent to 44 per cent of the total reliable run off.
In 1940, total water use was about 1000 cubic kilometres a year. It had doubled by 1960 and doubled again by 1990. The rising need for water has two components: One is that more and more people use water and the other is that they use more of it than they used to.
The Qur’an reminds us that water is the source of all life. “Do not the unbelievers see that the heavens and the earth were joined together, then We clove them asunder and We made every living thing out of the water? Will they not then believe?” (21:30).
The phrase can equally mean that every living thing is made of water (as its essential component) or that every living thing originated in water. The meanings are strictly in accordance with scientific data. Life is indeed of aquatic origin and water is the major component of all living cells. Without water, life is not possible. When the possibility of life on another planet is discussed, the first question is always: Does it contain a sufficient quantity of water to support life?