Fresh water is as essential to life as air, food, and sunlight. Much of the human race is painfully aware of this because it lives in relatively dry countries. In the well-watered parts of Europe and America, however, everyday activity does not centre around a struggle for fresh water, and so it is taken very much for granted. We may know from our geography books that little rain falls on much of Asia, Australia, Africa, and many parts of both Americas, yet it is not easy to grasp what this means in human terms. When we have water at the turn of a tap for as little as £4.0s.0d. a year, it is barely credible that in parts’ of the Near East a housewife may walk over 10 miles each day to fetch a single jar of water for her family. But even in the temperate parts of Europe and America, water supplies are rapidly falling behind the enormous demands of industry, agriculture, and the domestic consumer, and water engineers are now considering how the even greater demands of the future are to be met.
Those who read this will almost certainly enjoy a piped water supply, and this alone makes it easy to have delusions about the amount of fresh water that is available to sustain life on the world’s land masses. The truth is startling: very little of the world’s water is usable. As much as 97.2 per cent exists in the oceans as salt water. The remaining 2-8 per cent is fresh water, but of this, 2-15 is solidified in polar ice-caps and glaciers, and cannot be used. Another 0.31 per cent lies so deep in the earth that it is uneconomic to pump it to the surface. We are thus left with a mere 0.34 per cent of the world’s total water that can theoretically be used—in rivers, lakes, and in the top half-mile of the earth’s crust.
This minute fraction of the world’s total is by no means easy to secure; it represents the amount that would be available if only we could intercept it. Much of it eludes us by draining quickly into the sea by way of rivers and below ground, and more still is wasted because it is too remote from the areas that need it. Almost without exception, there is a wet season with too much water followed by a dry season with too little; and there is hardly a single country over which rainfall is evenly distributed. Yet affluent countries use tremendous amounts of water throughout the year—in the dry districts as well as in the wet. To overcome these variables we have therefore to store the surplus water of the wet season for use during the dry, and to transport it long distances to where it is needed— both very expensive propositions.
Whereas in the past many countries were fatalistic, accepting that the vagaries of climate meant sometimes flood, sometimes drought, they are now slowly realizing that drastic steps must be taken if the next generation is not to run seriously short. Gradually, new laws are leading to a more efficient use of water through concentrating on waste prevention and on reuse. Also, new sources are being sought as part of a 10-year survey of water resources, started in 1965, called the International Hydro-logical Decade. We provide a background to many of the problems that water engineers will encounter. We explain the very unusual properties of this abundant fluid, and trace the history of fresh water from the moment the sun’s heat raises it out of the sea to the time when it returns whence it came. We also discuss water supplies, distribution, and purification, as well as the methods by which water can be used several times over before it escapes to the ocean.