About 10,000 years ago, most of the earth’s inhabitants were nomads who roamed in the neighbourhood of rivers and lakes, which provided not only drinking-water but also grazing along their banks. Several thousand years later, many people began to change their way of life: they started to live in settled communities.. In this new way of life, man’s basic requirements for food and water remained the same, but the means by which he obtained them had to change. First, he had to draw water continually from the same place. Second, to provide enough food for a settled population, he had to grow and tend crops; in other words, he started to farm. To do this successfully, he often had to supplement a scanty rainfall with river water, and so he began to work out the basic principles of irrigation.
In some parts of the world, man has never graduated beyond these first simple methods of water supply and irrigation. But in other parts, there grew up around 3000 B.C. a series of elaborate civilizations whose domestic and agricultural use of water was often more advanced than that of many developing parts of the world today. These civilizations evolved in areas of very low rainfall—specifically, in the valleys of the Tigris, Euphrates, Indus, Nile, and Yellow rivers. These rivers provided irrigation either by the natural flooding of the land, or by supplying water to man-made canals. Since seasonal floods occurred about once a year, at least one crop a year was harvested, except when the floods were so big that the crops were ruined. The peoples of these river valleys were compelled to use great ingenuity to overcome the double problem of obtaining enough water for domestic and agricultural use, and of preventing excessive flooding of the land.
After 3000 B.C. water began to be used in quite sophisticated ways—for baths, for water closets, and for irrigating pleasure gardens, such as the famous hanging gardens of Babylon. The bathrooms and W.C.s of Mesopotamia certainly made the fullest use of water, and waste water ran into brick-vaulted sewers under the streets, as it does today. Later, as the population increased, armies of slaves toiled to provide water in even greater quantities. Wells were dug to supply clean drinking-water; covered cisterns were built in cities to store water for use during dry spells; and canals were dug to bring water from further afield, like the 50-mile canal that brought upland water to Nineveh. The canals were not made simply by digging trenches in the crude manner of the 18th century in Europe, but were carefully constructed of stone or brick, and waterproofed with bitumen. It was as if life in areas of low rainfall inspired these ancient peoples to devise the most ingenious ways of exploiting water; we see the same determination today in the arid areas of Israel and in the west of North America.
Yet while these ancient civilizations developed their water supplies, they also warred with one another. Gradually the water systems that had taken so much time and knowledge to construct crumbled into ruin. After the fall of the Roman Empire, the dark age of water began, and if there were communities that used water to the full, they were few and far between. It was not, in fact, until the late 19th century that man once more reached the standard of water use set some 5000 years before.
When at last, in the 19th century, men began to build new water supplies, it was not on the sites of the old eastern civilizations; the scene shifts mainly to Western Europe and America. Here the water engineers’ problems were intensified by the rapid growth in population that followed the Industrial Revolution. Whereas before, most people lived in villages and small towns, where there was little danger of depleting or polluting water sources, large populations were now mainly concentrated in industrial cities, where water was often in short supply or polluted. So in spite of the comparatively heavy rainfall in many parts of Europe and America, the new cities began to run short of water, and had to be content with a spasmodic supply, of a quality that neither the Romans nor the Assyrians would have tolerated.
The rapidly increasing population also meant that, after the 19th century, communities were no longer free to move to areas with better water resources. When, for example, the Euphrates and Tigris changed their courses, new cities were built on different sites. This is obviously impossible today, for not only are most potential new sites already occupied, but our cities are too large and complex to abandon. We are therefore confronted with the problem of conveying large quantities of water to already existing cities, often for hundreds of miles, and of transporting water to buildings through a pipe network.
Only 400 million of the 2400 million people living in Africa, Latin America, and Asia receive piped water; most of this piped supply ends in a public outlet at the end of the street, and is by no means constant. In countries with a high standard of living, most houses receive piped water, and also possess wash-basins, W.C.s, and baths. But these amenities, which we now take so much for granted, are very recent innovations: a century ago a single outdoor tap supplied a whole street, and as recently as 1920 only one third of the houses in Britain had a water closet.
Today, we expect a very high standard from our water supplies. Our first requirement is quality—that is, water should be palatable, oxygenated, colourless, odourless, and free from organisms and harmful salts. Next in importance after quality is quantity, and to stress the inconvenience caused by a prolonged reduction in supply, we shall now look at a few figures for water consumption in the home. For a reasonably well-off British citizen, the average daily consumption of water in gallons can be broken down approximately in the following way: drinks, 0.5; flushing W.C.s, 10; personal washing and cleaning teeth, 8; waiting for water to run hot, 4; baths , 6; cooking and washing dishes, 5; cleaning house, 1; washing clothes, 4; cleaning car, 0.5. This amounts to a daily total of 39 gallons.
These figures refer only to the actual use of water in the home. The really significant figure, however, is the amount actually entering the mains from the treatment works. This always exceeds the amount actually used, because it includes leakage from pipes and from domestic fittings, which totals about 8 gallons per head per day in efficiently run water undertakings.
In Britain, the total consumption from the mains is 55 ghd—33 gal. for the domestic consumer and 22 gal. for industry. But in the next three decades this is likely to reach 100 ghd, a figure already approached in Stockholm, Berlin, Moscow, Paris, and Rome.
In many parts of the U.S.A. the domestic consumption exceeds 150 ghd. In some areas this figure is partly due to excessive wastage, either by the consumer or by leakage from pipes. Americans also make more demands on their supply than Europeans: air-conditioning consumes large amounts of water; automatic washing machines swallow 30 gallons per wash; garbage grinders require tap water to dispose of kitchen waste; W.C.s use 6 gallons per flush compared with 2 in England. The heaviest consumers in America are perhaps located in the arid parts of California, where water has become a status symbol. Here we find lush gardens, including lawns with built-in sprinklers and exotic swimming pools. Many would label these extravagant luxuries, but Californians pay for the water they use by meter, so it seems fair that they should be free to use as much as they can afford, provided they do not deprive others in need.-This argument, of course, applies only where the water sources are able to cope with such high demands; if they run dry, then desalination may be the only alternative.
Our third requirement of a domestic supply is that water should be provided continuously, and at a high enough pressure to reach with ease the top floor of an average house. Owners of tall buildings must fix booster pumps to lift water to the upper floors. A continuous water supply at high pressure is also essential for fire-fighting, although fire-engines also have booster pumps. Access to water for fighting fires is particularly important in cities, where one fire may easily spread to adjacent buildings. Water authorities therefore install fire-hydrants at intervals along streets so that any fire can be quickly hosed with mains water.
Enough water to sweep waste matter along the sewers is essential to prevent filth and disease. Some of this transport water enters sewers from W.C.s, wash-basins, baths, and some from factories; a large amount of rain may also enter many sewers via street drains. Sometimes, during severe drought, there is not enough water for the transport of sewage. When this happened in Western Europe during the drought of 1921 and in New York in 1965, chemical deodorizers had to be injected into the sewers at great expense.
We now move on to the water requirements of industry, which in Britain account for about 40 per cent of the total water consumption from water authorities. Nearly two thirds of industrial water is used for cooling and condensing: one ton of steel requires between 10,000 and 50,000 gallons for its manufacture; some chemical products may need 40,000 gallons per ton. The textile and paper industries are also large consumers, needing about 22,000 gallons for one ton of product. Water is often an ingredient in food making: for example, lb. of water is added to every 1 lb. of flour to make bread. All these types of industry are necessary for the kind of civilization that we have chosen for ourselves. In the future there will be even heavier demands on the water supply as industrialization and population increase.
In times of drought, or when the river level is low, the consumption by industry sometimes affects the domestic supply of water, but for economic reasons, industry inevitably takes precedence over the domestic consumer. All that is required of industry is to reduce water waste to a minimum and to return what is left to the river in a fit state for use by other consumers. A steel works may use 30 million gallons per day, and return it in a re-usable condition; or it may use only 1 mgd 30 times over, by which time it may be so contaminated that it requires special treatment before discharge into the river. In Europe and America increasingly severe regulations are being drawn up and slowly put into effect, which force industry both to re-use water and to purify its effluents.
Most industries require good quality water, but their standards are often different from those of the domestic consumer. The householder wants water free from harmful organisms; industry is more concerned with its mineral content. Sometimes, as in launderies, only a few minerals need be removed, which is simply done by a water softener. Water used in high-pressure boilers must be almost completely demineralized, however, otherwise heat and evaporation will precipitate and concentrate salts into a thick insulating scale in boilers and pipes. This scale is expensive to remove; it also seriously reduces the conductivity of heat-transferring surfaces and raises the temperature of the metal to a level where it may deteriorate. In the pharmaceutical industry, water is completely demineralized by treble distillation.
In the manufacture of food and drinks, water must be free of organisms and also of certain minerals and organic compounds. These substances, which are sometimes present in the domestic water supply, may not be noticed in a glass of water, but when incorporated into food and drink they may produce turbidity, and unwanted tastes and odours.
In many parts of the world, enormous quantities of water are needed for irrigation; in fact, most of the world’s food is produced in those regions that are already irrigated. Many parts of the world need irrigation to prevent a small population from starving. There are parts of Africa, for example, that have no rain for several years. Botswana, for instance, entered its fifth year of drought in 1966. Without water, harvests fail, cattle die by the thousand, and children die of malnutrition, or from pneumonia and enteritis brought on by lack of food.
Other areas of low rainfall, such as the valleys of the Nile, Tigris, and Indus, at least have the benefit of river water. Natural flooding of the land, or the deliberate diversion of water through canals, enables crops to be sown, harvested, and stored for the dry season. And because the annual peak river flow is fairly reliable, there is enough water for a large population to live at a low standard. The achievement of a high standard of living in areas of low rainfall, however, requires more than just cheap labour; it needs special technical knowledge, and enough money, carefully applied, to develop and maintain water storage and irrigation systems. With the aid of these, apparent miracles can be performed, as can be seen in California and in Israel.
Many parts of the world are now short of food because their populations have grown too large to be fed by locally grown crops. The position is different in well-developed countries with a high rainfall, where large populations are fed by using irrigation to produce a maximum crop yield. We are therefore faced with the possibility that, as populations increase, not only may supplies of fresh water become insufficient, but also food supplies may run short. This is an insuperable problem in places where populations and water consumption are increasing at the rate of more than 5 per cent a year. Industry and the domestic consumer may have enough water for a long time to come, but it is unlikely that there will ever be enough water to irrigate more than a small fraction of the earth’s surface, even if all the present water sources were economically exploited. The amount of water needed for irrigation is enormous—a square mile of cropland lacking 12 inches of rain would need 174 million gallons. To make matters worse, most of it cannot be re-used because it is lost by evapotranspiration, by percolation into the ground, and by becoming part of the crop itself. So far we have concentrated mainly on the problems of supplying enough water. But the fact that water is rarely present in the right quantity, at the right time, and at the right place may also result in there being far too much. Most countries have suffered from floods that have destroyed human and animal life, property, and crops. The control of floods, however, is often more difficult than providing a secure water supply. In the past, many cities developed along the fertile plains of large rivers, which conveniently afforded the benefits of a water supply, cheap navigation, and a means of removing sewage. There are no longer such compelling reasons for building on flood plains, yet the cities that remain are expanding, so that when flooding does occur the damage is correspondingly greater. In America well over 300 million dollars are spent each year to make it profitable to continue living on flood plains. In some areas serious floods are so rare that it would be uneconomic to spend large sums to prevent them. When, for instance, the Thames flooded parts of London in December 1965, the small damage caused was tolerated because the cost of prevention would have exceeded the cost of repair.
Protection must be provided from the catastrophic flood, however. One method of control, used in the Tennessee Valley scheme , is to store floodwater in reservoirs; the water is then allowed to flow gradually downstream over a long period of time. Another method, adopted on the lower Mississippi, is to cut canals across river loops, which increases the river’s gradient so that more water flows in a given time. By far the commonest device is to enclose the river with walls high enough to prevent water overflowing. The lower Mississippi has over 2500 miles of these walls, 30 feet high in places. But like many rivers that carry high seasonal flood-waters, the bed of the Mississippi silts up, and the walls have to be continually raised. It is for this reason that the city of New
Orleans, for example, lies below river level. If we have sometimes seemed to dwell too long on economics, it is because the main object of any water supply system is to secure water at the lowest possible cost. The price we pay for water is really very low considering the enormous cost of dams, reservoirs, treatment works, and pipe-lines. The main reason for the low cost of water is our willingness to share its benefits with others; the expense of individual schemes for each house or small community would be prohibitive. Also, we owe a great deal to technological improvements, notably the development of pipes that leak less and last longer. Even so, we must be prepared to pay more in the future. Expanding populations require more water, and since most of the near sources are fully exploited, this will mean tapping distant sources, at considerable expense. In many places, the domestic metering of water would discourage wastage; it is estimated, for example, that metering the domestic supply in New York would reduce consumption by 40 per cent. But many city dwellers want it both ways—to continue their large consumption, and still pay a low rate. The success of future water supplies thus not only depends on the application of new techniques; it also relies on educating the public to appreciate the value and the cost of water, which at present they take too much for granted.