The UNI EN 12845 requirements for water supply systems essentially mean understanding what information must be included in the design when the supply system consists of a pump station and a tank.
In this response, we organize the requested information so that it can be used as a practical checklist for project documentation.
Table of Contents
Where the rules specify what must be included in the design (section 4.4.4)
Section 4.4.4 of the rules specifies what information must be provided during the design phase regarding the selected water supply system.
When the water supply system consists of a pump station and a tank, the specific sections to refer to are 4.4.4.4 and 4.4.4.5, in addition to the general requirements for drawings and calculations (4.4.4.1 and 4.4.4.2).
UNI EN 12845 requirements for water supply: drawings (4.4.4.1)
Water supply drawings must show:
- the water supply lines and piping up to the control station;
- A key to the symbols.
In addition, the drawings must also show:
- location and type of shut-off valves and check valves;
- any pressure-reducing valve;
- water meters;
- backflow prevention devices;
- any water supply connection for other services.
The goal is to avoid ambiguity: it is not enough simply to “know” that a component exists; it must also be located and identified in the drawings.
Hydraulic Calculation (4.4.4.2): What It Must Demonstrate
In addition to the drawings, the hydraulic analysis must be included.
The hydraulic calculation must demonstrate that the minimum specifications of the water supply are sufficient to provide the required pressure and flow rate to the control station.
In practical terms, this step links the choice of fuel supply system (pumps/tank) to the performance verification: the declared and/or rated data are not “isolated,” but must be consistent with the performance required at the specified delivery point (inspection station).
Automatic Pumping Unit (4.4.4.4): Required Data
For automatic pump groups, the following characteristics and curves (among others) must be specified:
- Q/H characteristic curve of the pump, assuming an inlet level equal to the minimum level “X” (see Figures 4 and 5 in Chapter 9).
- Power consumption curve; for pumps with an increasing power curve (in short: centrifugal pumps), the power curve must be available up to NPSHr = 16 m.w.c.
- Required NPSH curve. For centrifugal pumps, the curve must be available up to NPSHr = 16 m.w.c.
- Statement of the available power for each engine.
- Available and required NPSH at the maximum expected flow rate.
- Minimum submersion depth for VTP pumps and Submersible Electric Pumps.
- For fully calculated networks: the pressure-flow curve required for the most and least favorable hydraulic operating areas.
Operational note: In the project documentation, it is advisable to keep this information as a single “package” (curves + statements), because these elements are interdependent: for example, the Q/H value must be interpreted in conjunction with the conditions at level X and the NPSH data.
Storage Tank (4.4.4.5): Required Data
For storage tanks, the following characteristics (among others) must be provided:
- Total volume.
- Actual capacity and range.
- Flow rate for tanks with reduced capacity.
- Vertical distance between the pump shaft and the minimum level “X” in the tank (see Fig. 4 in Chapter 9).
- Design Features of the Tank and Cover.
- Recommended frequency for scheduled maintenance that requires draining the tank.
- Protection against freezing.
- Minimum level “X” and normal level “N” (see Fig. 4 in Chapter 9).
The key point here is that it’s not just “volumes” that are required: levels, distances, and maintenance management are also required—that is, information useful for describing how the tank operates over time and under operating conditions (X/N).
Figures 4 and 5 + Table 12: Levels, Rooms, and Minimum Distances
Figure 4 is referenced for the effective capacity of the inlet tanks and the dimensions of the inlet chambers, distinguishing between conditions with and without an inlet well. The same figure also includes information such as:
- Effective capacity
- Minimum distance from the inlet pipe to the minimum water level
- Minimum distance from the inlet pipe to the bottom of the sump
Fig. 5 illustrates the design of the sedimentation and inlet chambers, including components such as filters, water level “X,” the sedimentation chamber, the inlet chamber, and various feed methods (weir, open channel, conduit/pipe).
In addition, Table 12 specifies the minimum distances for the placement of the inlet pipe (as shown in the figures). It is also noted that, if an anti-vortex plate with the minimum dimensions specified in Figure 12 is installed, dimension A may be reduced to 0.10 m. It is also noted that a tank may be equipped with a socket to maximize its effective capacity.
Table 12 — Minimum Distances (as shown)
| Nominal pipe size (mm) | Minimum B (m) | Minimum without anti-vortex plate (m) | Minimum with anti-vortex plate (m) | Minimum size of anti-vortex plate A (m) |
|---|---|---|---|---|
| 60 | 0.08 | 0.25 | 0.20 | 0.10 |
| 80 | 0.08 | 0.31 | 0.20 | 0.10 |
| 100 | 0.10 | 0.37 | 0.40 | 0.10 |
| 150 | 0.10 | 0.50 | 0.60 | 0.10 |
| 200 | 0.15 | 0.62 | 0.80 | 0.10 |
| 250 | 0.20 | 0.75 | 1.00 | 0.10 |
| 300 | 0.20 | 0.90 | 1.20 | 0.10 |
| 400 | 0.30 | 1.05 | 1.20 | 0.10 |
| 500 | 0.35 | 1.20 | 1.20 | 0.10 |
Final Checklist: What to Prepare to Avoid “Gaps” in the Project
For a water supply system using pumps and a tank, the design documentation should include at least the following:
- Complete drawings up to the control station, including a legend and components (valves, reducers, meters, backflow preventers, and other equipment).
- Hydraulic calculation demonstrating the required pressure and flow rate at the control station.
- For the pump group: curves (Q/H at level X, power consumption, required NPSH), power per motor, available/required NPSH at maximum flow rate, submersion depth (VTP and submerged), and—if the system has been fully calculated—pressure/flow rate curves for the most favorable and least favorable areas.
- For the tank: volume, effective capacity/range, backup flow rate (if capacity is reduced), vertical distances and X/N levels, construction/coverage, maintenance involving draining, and freeze protection.
- Refer to Figures 4 and 5 and Table 12 when describing rooms, levels, and distances of the inlet piping.
Conclusion
During the design phase, the requirements are translated into a coherent set of drawings, analyses (hydraulic calculations), and technical data on pumps and tanks (curves, levels, distances, management). Organizing this information from the very beginning helps make the design process more manageable and verifiable.
