water supply


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water supply,

process or activity by which water is provided for some use, e.g., to a home, factory, or business. The term may also refer to the supply of water provided in this way.

In the United States, the average residential daily water supply demand is 100 gal (380 liters) per person, although it can go as high as 500 gal (1900 liters) per person. The stringency of the requirements that a supply of water must meet depends on the use to be made of it. For example, water used to wash semiconductor material from which transistors are made must be extraordinarily pure. The more usual requirements, however, are that water be free enough of harmful bacteria, chemicals, and other contamination to be drinkable; free of substances that make its taste or appearance unpleasant; and if the water is to be used for washing, free of salts of calcium and magnesium that will interfere with the action of soap.

The basic source of water is rainfall, which collects in rivers and lakes, under the ground, and in artificial reservoirs. Water from under the ground is called groundwater and is tapped by means of wellswell,
aperture in the earth's surface through which substances in a natural underground reservoir, such as water, gas, oil, salt, and sulfur, can flow or be pumped to the surface. In the United States, until some years after the Civil War, the majority of wells were "open," i.e.
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. Most often water must be raised from a well by pumping. In some cases a well will draw water from a permeable rock layer called an aquifer in which the water is under pressure; such a well needs little or no pumping (see artesian wellartesian well,
deep drilled well through which water is forced upward under pressure. The water in an artesian well flows from an aquifer, which is a layer of very porous rock or sediment, usually sandstone, capable of holding and transmitting large quantities of water.
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). When the groundwater that is extracted is replenished slowly or not at all, the aquifer is depleted and deeper wells, or new water sources, are needed. (The depleted water-bearing layer can also compact, leading to subsidence at the surface.) Water that collects in rivers, lakes, or reservoirs is called surface water. Most large water supply systems draw surface water through special intake pipes or tunnels and transport it to the area of use through canals, tunnels, or pipelines, which are known as mains or aqueducts. These feed a system of smaller conduits or pipes that take the water to its place of use. The California Water Plan, initiated in 1957, eventually entailed twenty dams, seven power plants, and more than 700 mi (1100 km) of canals, tunnels, and pipelines to meet the needs of southern California residents—a total of more than five billion cubic meters of water per year.

A complete water supply system is often known as a waterworks. Sometimes the term is specifically applied to pumping stations, treatment stations, or storage facilities. Storage facilities are provided to reserve extra water for use when demand is high and, when necessary, to help maintain water pressure. Treatment stations are places in which water may be filtered to remove suspended impurities, aerated to remove dissolved gases, or disinfected with chlorine, ozone, ultraviolet light, or some other agent that kills harmful bacteria and microorganisms. Sometimes hard water is softened through ion exchange, by which dissolved calcium and magnesium salts are replaced by sodium salts, which do not interfere with soap. Salts of iodine and fluorine, which are considered helpful in preventing goiter and tooth decay, are sometimes added to water in which they are lacking.

Not all water supply systems are used to deliver drinking water. Systems used for purposes such as irrigation and fire fighting operate in much the same way as systems for drinking water, but the water need not meet such high standards of purity. In most municipal systems hydrants are connected to the drinking water system except during periods of extreme water shortage. Because many cities draw water from the same body into which they discharge sewage, proper sewage treatment has become increasingly essential to the preservation of supplies of useful water (see seweragesewerage,
system for the removal and disposal of chiefly liquid wastes and of rainwater, which are collectively called sewage. The average person in the industrialized world produces between 60 and 140 gallons of sewage per day.
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; water pollutionwater pollution,
contamination of water resources by harmful wastes; see also sewerage, water supply, pollution, and environmentalism. Industrial Pollution
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).

Water Supply

 

the aggregate of measures for providing water to various consumers—the public, industrial enterprises, transportation, and so on. The complex of engineering installations that perform the tasks of water supply is called the water-supply system. All modern systems of water supply in population centers are centralized: each of them provides water to a large group of consumers.

Modern water-supply systems are divided into public and production (industrial or agricultural) types, depending on the purposes of the installations that are served. The most important consumers of water are enterprises in the metallurgical, chemical, and petroleum-refining industries, as well as steam power plants. Certain measures associated with the use of water do not, according to their classification, belong to water supply. For example, the supply of water for agricultural fields is a special branch of water conservation (irrigation), and supplying water to the turbines of hydroelectric power plants belongs to the area of hydroelectric power engineering.

Natural water sources—surface, or open, bodies of water (rivers, reservoirs, lakes, and seas) and subterranean (ground and artesian waters, as well as springs) bodies—are used for water supply. Subterranean water is the most suitable for public needs. However, subterranean sources often prove to be insufficient to supply water to large population centers, and obtaining large amounts of water from them is economically unfeasible. Therefore, surface sources of fresh water are used, for the most part, to supply water to large cities and industrial facilities. The following installations serve to obtain water from natural sources, as well as to purify it according to the needs of consumers and to convey it to the places of consumption: water-intake installations, first-stage pumping stations (which convey water to places where it is purified), purification installations, collection reservoirs for pure water, pumping stations of the second and later stages (which convey purified water to cities or industrial enterprises), and water conduits and water-main networks (which convey water to consumers). The general water-supply plan (see Figure 1) may change its form depending on specific conditions. If, for example, the water from a given source does not require purification, the purification and related installations are omitted from the plan. When the source is located at a point that is higher than the facility being sup-plied with water, the water may be conveyed by gravity flow, and therefore pumping stations are unnecessary. The location of water towers and pressure reservoirs depends upon local terrain. In certain systems several sources of water supply are used, which leads to an increased number of basic installations. When there is a great diversity of elevation on the territory to be supplied, a so-called zone system of water supply—that is, individual networks for regions of the city at various elevations, with separate pumping stations—is created. Sometimes water-lifting pumping stations, which

Figure 1. General diagram of water supply

take water from the city’s main network and convey it to elevated regions, are installed.

Water-intake installations have different equipment depending on the type of water-supply sources and the local conditions. River, reservoir, lake, and sea water intakes are used to take in surface waters; depending on the depth of the water-bearing strata, tubular (drilled) wells or horizontal drainage systems (drain pipes or tunnels located within the water-bearing stratum) are used to take in subterranean water. Spring waters are collected by means of capping installations (stone tanks, receiving chambers, and so on) located at the point where the spring water is discharged with the greatest intensity.

In most cases, water is raised from subterranean sources by centrifugal pumps. Submersible pumps, which are lowered beneath the water level into a well and are equipped with an electric motor that is sealed in a waterproof casing, are very efficient. When artesian (head) waters are being used, the level of the water in the well is established above the water-bearing layer after the well has been constructed. Sometimes the pressure in the layer is so great that the water flows up by itself out of the well and onto the surface. For municipal water mains in which subterranean waters are used, a group of wells is usually installed. The water from these wells flows into a storage tank and from there is sup-plied to consumers by a pumping station. Shaft wells are used when the subterranean waters are relatively near the surface. Depending on the depth of the shaft wells, water is raised from them by standard or submersible pumps. In the water-supply systems of population centers, water-intake installations of all types are included within the public-health protection zone.

As a rule, pumping stations of modern water-supply systems are equipped with electrically driven centrifugal pumps; they also have control, safety, and metering devices. Many pumping stations have remote control and are fully automated.

Purification installations process natural water for the pur-pose of imparting to it the qualities required by the consumers. The purified water is conveyed to its destination through water conduits and is distributed throughout the territory by means of a water-main network. The street network is connected to house branch pipes, through which water is brought into buildings. A network of interior water pipes that distribute the water to the points of its discharge through various outlet units (faucets) is set up within the buildings. In well-designed apartment houses and in some public buildings, there are also systems that supply consumers with hot water. In production buildings water is distributed to various technical units, machines, equipment, boilers, and so on. The distribution of water is also partially accomplished from the external (street) network by means of standpipes. Water for extinguishing fires is furnished from outdoor fire hydrants located along the street network. Interior fire-fighting outlets are also installed in public and production buildings, as well as in apartment houses of more than 11 stories.

Under certain conditions so-called circulating-water systems (see Figure 2), as well as systems with repeated utilization of water, are used for industrial enterprises. Circulating-water systems prevent the nonrational utilization and the pollution of natural waters. In such systems the water is supplied to the consumers again after suitable treatment (cooling or clarification). Cooling towers, spray ponds, and cooling pools are used to cool the water in circulating-water systems. In this type of system, water is taken from the source only to replace losses from cooling and irreplaceable expenditures in production. Thus, the quantity of water taken from the source in the circulating-water system is considerably less than in an ordinary once-through system. This occasionally makes possible the use of a natural source that, in a once-through system, would be insufficient for a given consumer. Systems of repeated utilization of water are used in cases when the water discharged by one production consumer may be used by another. This also decreases the quantity of water that must be taken from the source of the water supply.

Figure 2. Diagram of circulating water supply

As a consequence of the considerable growth of water consumption in population centers (as a result of the growth in the number of inhabitants, as well as the presence of many kinds of amenities) and in industry, local natural sources in some areas have become inadequate to satisfy the consumers’ demand for water. Such regions are supplied with water from distant sources. Thus, one of the sources of Moscow’s water supply is the Volga River, from which water is conveyed by canal over a distance of 128 km; the central regions of the Donbas are supplied with water by a canal and water conduits that cover a distance of 130 km.

Sanitary inspection. The quality of the water supplied to the public—over its entire transportation route, from the water-conduit station to the consumer—is subject to strict sanitary inspection. This inspection, which is carried out by regional and municipal public-health and epidemic-control stations, extends to all systems supplying general-use and drinking water to population centers, as well as other systems that deliver potable water. The bodies of the State Sanitary Inspection of the USSR have ratified the Statute on the Planning of Zone Sanitary Protection of Centralized Water Supply and Water Sources, which is mandatory for all organizations planning and building water-supply systems, as well as for all water-pipeline enterprises. On territory within the public-health protection zone, a system is set up to ensure the reliable protection of the water-supply source from pollution and the maintenance of the required water qualities. Planning for the public-health protection zones is an essential component of every water-supply project, without which it cannot be approved.

History. The history of water supply extends over several millennia. Even in ancient Egypt very deep wells were constructed to get subterranean waters; they were equipped with the simplest mechanisms for lifting water, and they used ceramic, wooden, and even metal (copper and lead) pipes. In ancient Rome there were already very large, centralized water-supply systems; aqueducts, which bridged ravines and valleys for gravitational-flow water conduits, have been pre-served. A water conduit made of wooden pipes, whose construction dates to the turn of the 12th century, was discovered during excavations in Novgorod. There is also information concerning a gravitational-flow water conduit made of earthenware pipes that was constructed in Georgia in the 13th century. In the 15th century a spring-fed water pipeline system was constructed for the Moscow Kremlin. The water-main systems in St. Petersburg, Peterhof, and Tsarskoe Selo were built in the first half of the 18th century. The installation of the first Moscow (Mytishchi) water conduit was completed in 1804, and the St. Petersburg municipal water-main system was completed in 1861. In 1902 a new Moscow water conduit was put into operation, with a water intake from the Moskva River near the village of Rublevo. A total of 215 cities in prerevolutionary Russia (about 20 per-cent of all cities) had centralized water-supply systems. During the years of Soviet power, water supply has been greatly developed, both in the number of water conduits and the length of water mains and in the amount of water supplied to the public and other consumers. By 1968 there were 1,600 cities and 2,520 workers’ settlements with centralized water supply, the length of water mains had increased by a factor of 34, and the total amount of water supplied through municipal water pipelines had increased by a factor of approximately 40.

REFERENCES

Fal’kovskii, N. I. Istoriia vodosnabzheniia v Rossii. Moscow-Leningrad, 1947.
Koniushkov, A. M. Vodosnabzhenie predpriatii tiazheloi promyshlennosti. Moscow, 1950.
Pokrovskii, V. N. Vodosnabzhenie teplovykh elektrostantsii. Moscow-Leningrad, 1950.
Ovodov, V. S. SeVskokhoziaistvennoe Vodosnabzhenie i obvodnenie, 2nd ed. Moscow, 1960.
Rukovodstvo po kommunal’noi gigiene, vol. 2. Moscow, 1962.
Abramov, N. N. Vodosnabzhenie. Moscow, 1967.

N. N. ABRAMOV

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