I. Answer the following questions:

1. What is water supply system?

2. What does indicate that ancient peoples were concerned with the water supply?

3. What did the ancient water systems include?

4. What distribution systems were popular in the 17^th /18^th centuries?

5. How was water filtrated in the 19^th century? Why?

6. What do usual water sources for modern supply system contain?

II. Find the English equivalents of the following phrases in the text:

• система доставки воды

• общественные нужды

• копать глубже

• достигнуть пика (верхней точки)

• акведук для подачи воды

• резервуары для хранения воды

• организмы (бактерии), появившиеся в воде

• загрязнение воды

• использование (применение) чугунных труб

• болезни, переносимые водой

• постройка дамб через реку

• поставка остается постоянной

III. Look at the groups of words below. Which word is the odd one?

1. a) supply b) conveyance c) distribution d) pollution

2. a) chlorine b) cast-iron c) lead d) stone

3. a) treatment b) storage c) disease d) distribution

4. a) compounds b) population c) peoples d) community

5. a) flow b) supply c) current d) stream

6. a) conveyance b) distribution c) pipeline d) supply

7. a) storage b) sources c) canals d) aqueducts

Water-supply system (II)

Modern aqueducts—comprising canals, closed tunnels, and large pipelines—deliver water by means of gravity in some cases, but usually some method of pressurization is used. After the water reaches collection points it is normally given some kind of treatment to improve its quality to a usable level. Most important is the purification process, which destroys harmful bacteria and deactivates viruses. Liquid chlorine is the most common chemical used in modern treatment plants and is usually applied before other treatment and as a final treatment before distribution. In some plants, ozone and ultraviolet light are used as disinfectants.

Water-treatment works employ a variety of other treatment processes, which include long-period storage, aeration, coagulation, sedimentation, softening, and filtration; these processes are used in varying combinations, depending primarily on the characteristics of the water but also on its intended use. Long-period storage, usually in reservoirs or setting basins, gives particulates a chance to settle out, and filtration through beds of fine sand or through crushed anthracite coal can trap the suspended matter. Different chemical additives cause particles to coagulate and thus to settle. Aeration mixes air with water either by spraying the water into the air or by forcing small air bubbles through the water and is used primarily to reduce unpleasant odours and tastes. Softening is the process of removing calcium and magnesium from the water either by chemical precipitation or by ion exchange.

In parts of the world where there is little or no fresh water, plants that desalt seawater, wastewater, and highly mineralized groundwater have been constructed. The methods used to remove salt from water include distillation, in which salt water is evaporated and fresh water is condensed; crystallization, where salt water is frozen in such a way that salt-free ice is formed and then thawed; and a membrane process, where the membrane filters the salt ions from the water. The first large desalting plant was built in Kuwait in 1949. Subsequent technological advances have allowed for larger, more efficient plants to be built. One plant near Tijuana, Mexico, has a daily capacity of 7,500,000gal.

After treatment, water is pumped either directly into the distribution system or to an elevated storage location, such as a water tank. For adequate distribution, water systems must operate under pressure. In some cases, the gravity drop of water from its elevated storage location provides enough pressure; otherwise, it is supplied by a pumping station. Adequate pressures range between 30 and 100 pounds per square inch (2 and 7 kilograms per square centimetre). Many communities base water-pressure requirements on what is thought to be adequate to fight fires, where pressures of up to 75 pounds per square inch are sometimes necessary. Materials used in transporting water to homes and industries include pipes of cast iron, steel, concrete, and asbestos cement. Meters record water usage at the site of consumption, and charges are levied to help pay for operation and maintenance of the system.