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“What pump do I need for a 10-metre well?” is a question that has kept coming back on Italian forums for years [5][6]. The first thing to know is how deep the water is, not how deep the well is: measure it with a weighted string, with the pump off and again after drawing water, because the level drops when you pump.

The limit of surface pumps

A surface pump does not push the water up from the bottom: it creates a vacuum in the hose and lets atmospheric pressure push the water up. That is why there is a physical limit. With standard atmospheric pressure of 101,325 Pa, the theoretical maximum water column is about 10.3 m. In practice it is always less: losses in the suction hose, altitude, water temperature and the tightness of the fittings.

The maximum suction depths declared in the data sheets we have collected:

With the water at 10 m a surface pump will not work, whatever head is printed on the box: head is about pushing on the delivery side, not about suction. You need a submersible pump, lowered into the well below the water level.

Which submersible pump

• Well diameter: “4-inch” well pumps are made to fit into casings of that diameter. Tank pumps have different dimensions: compare the external diameter on the data sheet with the internal diameter of the well.
• Maximum immersion depth: this tells you how far below the water surface the pump can sit, not the depth of the well. Also check that the cable is long enough.
• Head at the flow you need: the pump has to overcome the 10 m of the well, the height of the outlet, the hose losses and any pressure needed for the sprinklers.

An example with manufacturers’ curves

Water at 10 m, outlet 1 m above ground, 25 m of hose with a 25 mm internal diameter. Estimates with our calculator based on the published curves:

Open this example in the calculator and change the values to those of your well.

Two tank pumps that promise 4,000–4,700 l/h (67–78 l/min) on the box give from 12 to 38 l/min here, and are not enough for sprinklers that need 1.5 bar. These are estimates based on declared data, without fittings or valves: the real flow will be somewhat lower.

For the electrical installation, the control box and fitting the pump in the well you need an installer: here we deal only with the hydraulic choice.