Choosing a borehole pump: how to determine the right operating point (and prevent a dry borehole)

Most well pumps are chosen incorrectly on one point: the head is too narrowly estimated. Those who only consider the well depth and forget the sprinkler pressure and pipe loss end up with a pump that seems correct on paper but delivers no pressure in the garden. In this article, you will correctly calculate the operating point of your well pump, match the flow rate to your well's yield, and select the right model.

Start with the operating point, not the pump

You buy a well pump based on two numbers that together form the operating point: the required head (in meters) at the desired flow rate (liters per hour). Add these four items for the head:

1. Dynamic water level — not the static level, but the level during pumping. As soon as you pump, the water level in the well drops (drawdown). Calculate with the lowest level.
2. Geodetic height — the height difference from the water level to the highest tap point or sprinkler.
3. Pipe loss — friction in the riser pipe, hose, and fittings. This can add up significantly with long or thin pipes.
4. Working pressure at the tap point — the item most often forgotten.

Convert working pressure to meters: 1 bar is approximately 10 meters of head. An average sprinkler requires 2 to 4 bar, so 20 to 40 meters — and this comes on top of the well depth and pipe loss. This explains why a 12-meter deep well often requires a pump with 50 to 70 meters of head. The HOMA H802-H818 achieves up to 95 meters, giving you that margin.

Rule of thumb: overdimension the head, not the flow rate. Extra pressure costs little; too much flow rate will drain your well.

Match the flow rate to your well's yield

A well only supplies a limited number of liters per hour. If you pump more than the well supplies, the water level will continue to drop until the pump draws air and runs dry. Therefore, know the well yield (have it measured or test it) and choose a pump flow rate below that.

For irrigation, add up the consumption of all sprinklers running simultaneously. If that total exceeds the well's yield, divide the garden into zones that operate in turn — better than a stronger pump that drains the well.

Other things to consider

Well diameter and installation depth

4 inches (approx. 100 mm) is standard for drilled wells; check the actual internal dimension of your well casing. Hang the pump above the filter section and well below the dynamic water level, so that the motor is always cooled by flowing water.

Material and sand

Groundwater almost always contains fine sand, and sand is the number one source of wear. Choose a pump with a stainless steel housing, suction strainer, and impellers. For consistently high sand content, a full stainless steel version such as the HOMA H802 series or the SAER 4 inch deepwell is not a luxury but a necessity.

230V or 400V — and pay attention to cable drop

Lighter well pumps run on 230V; heavier ones on 400V three-phase power. The HOMA H802 series operates on 230V, which is convenient if you don't have three-phase power at the well. For a deep well, consider the voltage drop across the motor cable: the longer the cable, the thicker the conductor cross-section must be to maintain voltage to the motor. A cable that is too thin over 40 meters deep will cost power and reduce lifespan.

Automation: pressure tank or electronic control

If you want to use the well pump for water supply (faucet, toilet, washing machine), you make it fully automatic. Classically with a pressure tank and pressure switch; more modern with electronic control that maintains constant pressure and offers dry-running protection.

The most expensive mistakes at a glance

• Not including sprinkler pressure. The pump reaches the depth, but delivers no pressure to the sprinklers.
• Pump flow rate above well yield. The well drains, the pump runs dry.
• Using static level instead of dynamic water level. The level drops during operation; that's what you calculate with.
• Too thin motor cable for a deep well. Voltage drop costs power and shortens motor lifespan.
• Plastic pump in sandy water. Rapid wear — choose stainless steel.

Which well pump do we recommend?

IRRIGATION WITH HIGH PRESSURE

HOMA H802 - H818

Stainless steel, up to 95 m head, for wells from 4 inches, 230V.

from €893,95

View pump

SANDY WATER

SAER 4" Stainless steel well pump

Fully stainless steel 4 inch deepwell pump, robust and wear-resistant.

from €449,00

View pump

View the complete range of well pumps.

Frequently Asked Questions

How much head do I need for irrigation?
Add up the dynamic water level, the geodetic height, the pipe loss, and the sprinkler pressure. Convert sprinkler pressure with 1 bar being approximately 10 meters; a 12-meter well with sprinklers at 3 bar will quickly require 50 to 70 meters of head, such as the HOMA H802-H818 delivers.

Why does my well pump run dry?
Almost always because the pump flow rate is greater than the well's yield: the water level drops until the pump draws air. Choose a lower flow rate, divide irrigation into zones, or use dry-running protection.

Should I choose 230V or 400V?
230V is sufficient for lighter well pumps on a standard outlet. Choose 400V for heavier pumps or long lines; for deep wells, ensure a sufficiently thick motor cable to prevent voltage drop.

Why a stainless steel well pump?
Groundwater contains fine sand that quickly wears down plastic and cast iron. A stainless steel housing with a suction strainer and impellers lasts significantly longer in sandy water.