Современные проблемы промышленного и гражданского строительства на занятиях английского языка. Кузьмина Е.В. - 47 стр.

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great sewer. As a matter of fact it took 2 outbreaks of cholera to pass a Bill for

an improved water supply in the middle of the 19

century.

In spite of the progress made in the field of water supply in many

countries, there is much to be done yet. In Asia, Africa, Central and South

America outside the great cities, methods are primitive as ever they were;

village ponds are still used in Africa and Asia for drinking, washing and bathing

and as watering places for cattle, in Madagascar in recent years people have had

to carry their water bottles several miles and, as some of them can only do the

journey twice a week, they have trained themselves to do with the minimum of

water, drinking only on alternate days and never washing during a drought.

In Japan, running water is still a luxury, even in the great cities: the

average household has to carry water from a central source, while the villages

rely on springs and streams.

The speedy industrialization of our country has also made the problem of

water very acute.

TEXT B. PURIFICATION OF WATER SUPPLY.

Water taken from its natural source – the ground lakes of rivers – contains

many objectionable elements. It may possess gases of an obnoxious nature,

bacteria, mineral elements, mud, and suspended vegetable growths which

render it unpalatable. Some of these objectionable materials may be eliminated

readily, others require complex treatment.

The obnoxious gases are removed by aerating the water. Some of the

mineral elements, such as certain forms of iron, also are removed by this means.

The suspended materials require coagulation and settling process, and bacteria

are eliminated with the addition of chemicals and sand filtration. The mineral

elements which render the water hard must be separated by a chemical process

in which the objectionable element is replaced by one that is favorable. A

filtration plant may use one or a combination of all of these processes, the water

undergoing a complete change as it passes through the plant.

The processes generally employed in making water safe for water supply

include coagulation, filtration, and disinfection. Water from some sources must