The main task of the water supply is to transport water to consumers under the condition of the greatest convenience of its use, at the lowest cost, but high reliability in the operation of the system.

Internal water supply is a system of mechanisms that provide water supply to sanitary equipment, process equipment, and fire hydrants located inside the building.
The internal water supply system consists of the following devices: one or several inputs, water metering units, a network of pipelines (main, distribution, and liners), and fittings. In some cases, if necessary, the system includes local units to increase the pressure and spare tanks for hot water (water heaters).
The temperature of cold water in places of water collection should be not less than
5 ° C. The temperature of hot water can be in the range of 50-70 ° C, but should not exceed 75 ° C to avoid burns. In individual water heaters (boilers) the optimal temperature is 55-60 ° C, because at temperatures above 60 ° C, the heating element begins to be covered with lime, and at temperatures below 55 ° C bacteria (eg, legionella) in stagnant water intensively reproduce, and the water begins to smell bad and can be quite dangerous for some groups. For prevention, short-term heating of water in the boiler to 70-80 ° C is recommended, because at such temperatures the whole colony dies completely almost instantly (for comparison, at a temperature of 60 ° C 90% of the colony dies in just 30 minutes).
So, we understand that the internal water supply system is subdivided first of all into cold (B) and hot (T). In the diagrams and drawings in the domestic documentation, cold water pipes are marked with the letter of the Ukrainian alphabet “B”, and hot – with the letter “T”, but each of them also has its own varieties.

For cold water it is:
B1 – domestic and drinking water supply;
B2 – fire water supply;
B3 – industrial water supply (general designation).

Domestic drinking water pipes are designed to supply water that satisfies
DSanPiN 2.2.4-171-10 “Hygienic requirements for drinking water intended for human consumption”, for drinking, washing, bathing, cooking, and other household needs.

Fire pipes are designed to extinguish a fire or to prevent its spread. Water in fire-fighting water mains can be of non-drinking quality because the main requirement for it is the constant presence of water in the system and sufficient pressure.

Industrial water pipes are designed to meet the technological requirements of the production or facility. Such water mains can consist of several systems that provide water supply of different quality, pressure, quantity, depending on the requirements of the technological process.

Modern hot water must have two pipes in the house: T3 – supply (it is from this system and water collection is performed for consumers) and T4 – circulating (which is designed for constant circulation of hot water in the system so that the water temperature in the falling pipe was not less than admissible). Incidentally, we note that T1-T2 denotes heating systems (heating networks), which do not belong directly to the water supply. Depending on the mode and volume of hot water consumption for household needs of buildings and structures, hot water supply systems can be local or central.

Depending on the mode of water consumption and purpose of the building, as well as on the technological and fire safety requirements of the network are dead-end, ring, combined, zone.
• Dead-end networks are used mainly in buildings where water supply interruptions are allowed in the event of failure of part or all of the water supply network. These can be residential, public, and sometimes industrial buildings.
• Ring networks are used in buildings when it is necessary to ensure a reliable and uninterrupted water supply to consumers (in high-rise buildings, in houses with fire water supply, in industrial buildings, etc.). The ring networks are connected to the external water supply by several inlets, so that in case of disconnection of one of them the water supply to the house does not stop.
• Combined networks consisting of ring and dead-end main pipelines are used in large lines with a large spread of water collection devices.
• Zone networks are several networks in one building, not interconnected or separate. Networks of separate zones can have independent inputs and installations for the increase of pressure. In some buildings (high-rise) can be used the multi-zone network. At the lower point of the network (at the fittings) of each zone, in order to ensure its strength, the hydrostatic pressure should not exceed 60 m, and in fire water supply systems – 90 m.

No less important for the network of domestic and drinking water supply is the value of its maximum operating pressure – it should not exceed 0.6 MPa.