A quotation specifying twelve or fifteen metres does not show whether a surface pump will work well. Total construction depth describes where the bottom is. Static water level is measured once the water has settled, without pumping. Pumping water level is measured while pumping at a stated flow rate. All levels used in calculations must refer to a clear reference point, such as ground level. T02
Suction lift depends on the vertical distance from the water surface during operation to the pump inlet centreline. Resistance in the pipe, joints and other suction components adds to this. A long horizontal pipe is not the same lift as a vertical rise, but it also creates losses.
Why is an approximate 7–8 metre limit mentioned?
A surface pump cannot draw water without limit. Suction capability is limited by pressure conditions and the particular design. Grundfos educational material gives an example of up to 8 metres for self-priming jet pumps. This is not a guarantee for all units, and certainly not a universal permissible borehole depth. T08
A theoretical water column of approximately 10,3 metres at sea level follows from the relationship between atmospheric pressure and water density. This is a physical reference under ideal conditions, not a pump selection figure. A real system has losses and needs operating margin; temperature, altitude and pump characteristics also matter.
Two calculation examples
An example, not a site measurement. The bottom of the water needle is 16 metres deep. At rest, water settles 3 metres below ground; during pumping, 5 metres. The pump centreline is 0,5 metre above ground. The geometric suction lift during operation is therefore 5,5 metres, not 16 metres. Pipe losses and the selected model still need to be assessed.
A second example. The water needle is only 9 metres deep, but during pumping the water level falls to 8,5 metres below the pump. This is generally problematic for an ordinary surface pump set, even though the construction is shorter than in the first example. A more powerful motor does not remove this physical limit.
Does lowering the pump help?
The geometric distance may decrease, but this does not automatically permit a flood-prone pit or drilling beneath a building. Flooding, hygiene, electrical safety, maintenance and local requirements need assessing. A solution should not improve one figure by creating several new risks.
If the pumping water level is too deep for a normal surface system, a different construction or pumping technology is considered. An ordinary submersible pump often does not fit a traditional narrow water needle pipe. A system with a deep external ejector is also not the same as an ordinary pump set with an integrated ejector.
Before buying a pump, ask not for a promise of how many metres it will draw from, but for the water level, test flow rate and intended duty point. Read more in the explanation of a yield test.
Information sources
Choose a source to read its summary without leaving this page.
- T02
- T08
Sources checked on 2026-09-30. If the manufacturer has changed the product or documentation, follow the latest technical information for the specific model.