Water management 01.03.2020 10:27 01.03.2020 13:18
General recommendations for the installation of a water distribution system

A detailed calculation of interior water supply is carried out in accordance with the CSN 75 5455 standard.

In buildings with a small-scale water distribution system (houses, apartment buildings with max. 5 floors and a single stairway, from which the apartments are directly accessible, and up to five-storey office buildings with one staircase), the internal water pipeline can be designed using a simplified method in accordance with the ČSN EN 806-3 standard.


The so-called discharge units (LU) for each place where water is used are determined by this standard; the computational flow (Qd) is determined on the basis of the sum of LU and its highest value, the length and the diameter of the piping. Furthermore, the diameter of the supply pipe is determined by the required flow rate. The dimensions of the flowmeters and the stop-valves for water supply must also be determined by this flow rate.


It is important to bear in mind that e.g. a standard shower requires about 18 ÷ 22 l/min., the washbasin mixer up to 12 l/min, and pressure flushing even significantly more. For example the main 3/4"(DN 20) supply at a standard pressure has a maximum flow rate 50 l/min.


Controlled valves operate at a standard water pressure in the piping from 0.5 - 8bar (0.05 ÷ 0.8 MPa). All flow rates in the technical specifications are given for the line pressure of 3 bar (0.3 MPa).

If you want to maintain a long life of electromagnetic valves and a reliable operation of the equipment, you should respect the cross-sections of supply piping and follow the installation principles in accordance with the ČSN-DIN-EN 806 standard.


It is recommended to maintain the pressure in the distribution system at 2 ÷ 5 bar (0.2 ÷ 0.5 MPa). It is also recommended (in some countries even mandatory) to include in the mains a full flow filter with a 90um mesh (or less), e.g. the SLF01 (D) - 03 (D), SANELA.


A brief explanation of terms:



















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1 1/2





Nominal clearance DN, the piping diameter

The threaded steel or cast-iron piping and the threaded and flanged fittings are indicated in the drawings with nominal clearances DN. The abbreviation DN is usually not stated. Nominal clearance DN is a number indicating the approximate value of the inner diameter of the pipes and fittings in millimetres.

Piping made of plastic, copper, stainless steel or multilayer materials (plastic-metal combinations) are marked in the drawings with the outer diameter x wall thickness (da x s), the marks da x s or Ø are usually not mentioned.

On the right, the table shows the values of DN in millimetres and the corresponding diameter in inches.




The pressure range PN

The higher the number of the pressure range, the higher operating pressures are allowed.

The PN 20 range is recommended for the household distribution, the PN 16 pressure range is only used for the household distribution of cold and hot water (with limited maximum temperature).


The G thread and the R thread, the difference

G-threads have a cylindrical form in accordance with the EN-ISO 228-1 standard. R-threads have a conical form in accordance with the ISO 7-1 standard. If the thread size is 1/8", for example, the threads are specified as G1/8 or R1/8. Female G threads (cylindrical) can only be screwed into male G threads.

Female R threads (conical) can only be screwed into male G or R threads.