Lecture 1. Water-supply

1.1 Water-supply systems and schemes

System of water-supply is a complex of engineering structures, machines and apparatus, which are intended for water extraction from natural sources, improving its quality, its keeping, transportation and serving the consumers. The system consists of water receiving, barrage, cleaning, water pressure and regulating structures, highway headraces, separate networks and means of automation. According to local conditions, some of these structures may not be used or may not be connected with each other.

Water-supply systems are divided by such parameters: functional intention (economic-drinkable, productional, fire-prevention); sphere of service (united and separated); type of objects (urban, settlement, industrial, etc.); territorial occupation by water consumers (local, centralised, grouped); operation duration (temporal and permanent); type of natural source (with usage of underground or superficial water); means of barrage (gravitation and with mechanical water supplying); character of water usage (straight flowing, reverse and with repeated water usage); reliability of water serve providing.

Economic-drinkable systems of water-supply serve water for drinking, cooking and realization of sanitary-hygienic procedures. Water in this system should be of drinking quality. Production plumbing serves water on technological aims. The requirements to water quality are determined by technologists. Fire-prevention systems of water-supply are intended for water serving during extinguishing of fire. Water in fire-prevention systems can be of not drinkable quality. United plumbing satisfies necessities of all consumers, separated plumbing serves water for different necessities separately. Local systems serve water for separate water consumers (for example, for cattle farm, industrial enterprise, or separate group of buildings), centralised systems serve water for all consumers of the given settlement. Grouped, or district plumbing systems, are intended to serve water to a few settlements, farms or enterprises, which are removed from each other (they are designed, as a rule, in default of fresh water and characterised by a great length of headraces).

According to СНіП 2.04.02-84, water-supply centralised systems are divided into three categories by reliability of water providing. Economic-drinkable plumbing systems of settlements with number of habitants up to 5 thousands are referred to III category. The decreasing of water service not more then on 30% for the period of 15 days and less, and also interruption of water service during the repair not more than for 24 hours are allowed for them. II category is used for the number of habitants from 5 to 50 thousands. For them the interruption of water service can be up to 6 hours, and decreasing of serve cannot exceed 10 days. Settlement with the number of habitants about 50 thousands are referred to I category. For them the interruption of water service can be not more then 10 minutes, and decreasing of service cannot exceed 3 days. Category of water-supply system separate elements is determined basing on functional meaning in general water-supply system.

Mutual location of separate elements and structures in every certain water-supply system is named water-supply scheme. Choosing of structure composition depends mainly on the next factors: type of natural source and quality of water in it; category of water consumers and their requirements to the free pressures, volume and quality of water that is consumed; reliability of water serve; relief of locality.

Water-supply scheme from opened sources (fig. 1.1), as a rule, has the highest building cost and it is difficult enough in exploitation, as it needs presence of water-purifying and other buildings. By this scheme, water from the opened reservoir gets to water intake structures, from which it is given to the water-purifying buildings by the station first raising pumps. Quality of water is improved on water-purifying station, after that water is given into the reservoir of clean water (RCW), from which it is given to the plumbing water-supply network by the station second raising pumps thought the headraces. On the territory of settlement (usually at the highest places) the water-tower is built, which, like RCW, is intended for water storage, regulation of pumps’ work and maintenance of necessary pressure in network. Accumulation of water in tower takes place at time when pumps give more water then consumers use; water from tank is used up, when consuming exceeds the supply.

Underground water is often used for water-supply. This water (comparing with superficial water) has lower content of different admixtures, including radioactive admixtures, and also simpler composition of plumbing buildings. If quality of underground water doesn’t satisfy consumers’ requirements (for example, increased content of iron admixtures), the scheme with water-purifying (fig. 1.2) is used; if underground water by its physical-chemical and sanitary indexes satisfy the requirements of drinking water, then the simplest scheme of water-supply is used (fig. 1.3).

Fig. 1.1 Water-supply scheme from superficial sources (river)

1-river water intake; 2-pump station of the I rising; 3-water-purifying station; 4-reservoir of clean water; 5-pump station of the II rising; 6-headraces; 7-water-tower; 8-plumbing network; 9-water-supply object; 10-piezometric line in network at time of the maximal water consuming; 11-the same at the time of maximal transportation of water to the tower.

Fig. 1.2. Water-supply scheme with underground water purifying:

1-aquiferous layer; 2-mining hole; 3-water-purifying station; 4-reservoir of clean water; 5-pump station of the II rising; 6-headraces; 7-water-tower; 8-plumbing network; 9-water-supply object; 10-piezometric line in network at time of the maximal water consuming; 11-the same in headraces.

F ig.1.3. Water-supply scheme from the mining hole:

1-water intake mining hole; 2-deep electro-pump; 3-base above the mining hole; 4-headraces; 5-water-tower; 6-piezometric line in headraces at time of the maximal water consuming; 7-the same in the network; 8-water-supply object; 9-plumbing network.

Settlements near foot of mountains can have the water source that is located higher them. In this case self-watering water-supply system with or without water-purifying system is used.

Industrial enterprises are differed by their variety of technological processes, consume water of different quality and require different pressure in separate workshop networks. Specificity of water-supply technical systems is a possibility of water turn for different requirements. That’s why, water-supply systems of industrial enterprises are quite difficult. If enterprise is located on the territory of the settlement and consumes insignificant volume of not drinkable water, then it’s sufficient to serve water to the enterprise from the urban networks. If significant volume of not drinkable water is consumed, then it’s sufficient to organize separate systems of technical water-supply: straight flowing (fig.1.4a), in which water after the non-permanent use is thrown down in the sewage system; with repeated water usage (fig.1.4б), where water is used consistently in several technological operation; reverse (fig.1.4в), in which after the usage of water for the technical requirements, it is cleared and cooled, than used at the same object in the same technological operations. Choosing of technical water-supply scheme should be decided by technically-economic calculations.

Fig.1.4 Technical water-supply schemes

1-river; 2-water intake structure; 3-water-purifying structures; 4-pump station; 5-technical water; 6-enterprice; 7-sewer water; 8-water-purifying station; 9-an upcast of water in the river; 10-distributive chamber.