Once people were content with water which they found in the rivers, lakes, streams and wells. But with development of the industry and population growth there was a necessity much more carefully to operate water supply, to avoid harm for health and a damage for environment.
Any settlement requires giving of pure fresh water for drink, cooking, washing and washing. Usually water take from the rivers, lakes or underground sources and subject to its processing to make suitable for drink. Various kinds of the processing are applied to removal of natural and anthropogenous polluting substances, thus used processes are defined by level and character of pollution.
water from the polluted river at first passes "Water supply" In typical system of water supply through a grid with large cells for clearing of floating dust, fishes and plants. After that it zakachivaetsja in the tank where it is stored within several weeks. In this time many large polluting particles settle on a bottom. Besides, the maintenance of harmful bacteria as substances which served in the river for them as food are spent gradually decreases. After a sediment for destruction of the remained bacteria chlorine and other chemical substances is added. In some countries instead of chlorine use ozone, and at small water-purifying stations water sometimes sterilise, treating to its action of powerful ultra-violet radiation. After that water passes through a grid with small cells for removal of small plants and other particles.
the Remained smallest particles of type of dead bacteria and grains of insoluble minerals because of which water can seem muddy or slightly tinted, leave in special tanks by means of processes of coagulation and flokuljatsii. Addition of sulphate of aluminium or iron sulphate forces particles koagulirovat (to gather), therefore the tank approximately to half is filled hlopeobraznoj with weight. This weight is called flokulirovannym as a deposit or is simple in flakes. From the top part of a tank pure water which again passes through filters for the further clearing is taken away. These filters are formed by the layers of sand lying on the basis from gravel or anthracite (a coal version).
After a filtration water usually aerate to increase the maintenance of the oxygen dissolved in it. It impacts to water fresher relish, and also lowers its acidity at the expense of removal of the dissolved carbonic gas. There are some kinds aeratorov. In jet aeratore water is forced through small nozzles in air space. Cascade aerator includes a number of steps on which water flows down.
No filtration allows to remove the substances dissolved in water. It mainly salts of calcium and to a lesser degree magnesium salt. These salts dissolved from adjournment in a ground, define rigidity of water. In district with especially hard water for removal of some of the dissolved salts sometimes use chemical processing, and only after that water arrives in pipes. But usually to consumers if they see in it necessity, it is necessary to establish own equipment for these purposes.
Before distribution on pipes water is again sterilised by means of chlorine or ozone. After processing the chlorine most part leaves by means of sulphurous anhydride, but its small quantity is left for struggle against the further pollution by bacteria.
In those parts of globe where fresh water stocks are insignificant, use sea water, deleting from it salt. This process named opresneniem, can be carried out in the most different ways. Often salty water boil, water rises in the form of steam, and salt remains below. After that steam is cooled and, being condensed, turns to pure water.