A bore pump that looks right on paper can still be wrong in the ground. If the flow rate is too high, you can overdraw the bore and run it dry. If the head calculation is off, you end up with poor pressure at the tank, trough or house. A proper submersible bore pump sizing guide helps avoid both problems by matching the pump to the bore, the pipework and the job it actually needs to do.
For most Australian properties, bore pump sizing comes down to four things: how much water you need, how far it has to travel, how much pressure is required at the end point, and what the bore can sustainably produce. Miss any one of those and the pump may short cycle, run inefficiently or simply fail to perform.
What a submersible bore pump sizing guide should answer
Sizing is not just about choosing kilowatts or picking a known brand. The pump has to suit the application. A domestic bore supplying a pressure system to a home behaves differently from a stock water setup feeding tanks and troughs. Irrigation adds another layer again, especially where demand varies across the day or between seasons.
The main goal is to find the duty point. That means the flow rate you need at the total head the system imposes. Once that duty point is clear, you can compare it against pump curves and identify a model that will operate in a sensible part of its performance range, not right at the edge.
Start with flow rate, not motor size
The first step in any submersible bore pump sizing guide is working out how many litres per minute or litres per hour you actually need. This is where many sizing mistakes begin. People often size to the biggest pump they can afford, assuming more output is better. In practice, too much pump can be just as problematic as too little.
For a house, the required flow depends on peak simultaneous use. Bathrooms, laundries, outside taps and irrigation points all matter, but they rarely operate at full demand at the same time. For stock watering, you may be filling tanks slowly across the day rather than chasing high peak flow. For irrigation, the flow should match the zone design, not the total property requirement.
The bore yield matters just as much as site demand. If the bore sustainably produces 35 litres per minute, there is little sense selecting a pump designed to draw 70. You may get that output briefly, but not reliably. In poor yielding bores, storage tanks often make more sense than sizing the pump for direct peak demand.
Calculate total head properly
Once flow is known, the next step is total head. This is the full resistance the pump must overcome, and it includes more than just depth. A common mistake is to measure the bore depth and assume that is the head. It is only part of it.
Total head usually includes the pumping water level, the vertical lift from that level to discharge point, friction loss through pipework and fittings, and any pressure requirement at the outlet. If you need to deliver water into a pressure tank system or maintain usable pressure at taps, that pressure must be converted into metres of head and included.
The pumping water level is especially important. Static water level is where the water sits when the bore is resting. Pumping water level is where it drops to while the pump is running. That drawdown can be significant. Sizing from static level instead of pumping level can leave you with a pump that falls short in real operation.
Friction losses are easy to underestimate
Pipe size, pipe length, bends, check valves and filters all add friction loss. Longer runs to tanks, houses or paddocks can change the duty point more than expected. Undersized delivery pipe will increase losses and can make a decent pump look weak.
This is why the pump and the pipework should be considered together. In some cases, moving up a pipe size gives a better result than moving up to a larger pump. It reduces losses, improves efficiency and can lower running costs over time.
Pressure requirements must be realistic
If the pump is feeding a tank, the pressure requirement may be minimal. If it is feeding a home, pressure expectations are higher. Showers, appliances and pressure controllers need a stable operating range. Irrigation systems may require a set pressure at the sprinkler or dripper line, not just at the pump discharge.
A good sizing result balances usable pressure with practical operating cost. Oversizing to chase high pressure everywhere usually creates unnecessary wear and power use.
Bore diameter and pump fit matter
A submersible bore pump sizing guide also needs to account for physical fit. Not every pump suits every bore casing. The pump diameter has to suit the internal bore diameter with enough clearance for installation and cooling.
Small casing bores can limit your pump options, especially where higher flow is needed. Motor cooling also matters. Many submersible bore pumps rely on water moving past the motor for proper cooling. In large diameter bores or low flow conditions, a flow sleeve may be required to maintain that cooling path.
Sand content is another practical issue. Bores producing sandy water can shorten pump life quickly if the pump is not suited to those conditions. In those cases, material selection, intake position and bore development all become part of the sizing discussion.
Match the pump curve to the duty point
Once you know the required flow and total head, you can assess pump curves. This is where technical selection becomes more precise. Every pump has a performance curve showing how much water it can deliver at different heads.
The best choice is rarely the biggest pump that crosses your duty point. Ideally, the duty point should sit in a stable and efficient part of the curve. If it sits too far left or right, performance can be poor and operating stress can increase. Motor loading, efficiency and run time all need consideration.
This is also where voltage, phase and control method come in. Single phase may suit many domestic and small rural jobs, while larger agricultural or commercial systems often move to three phase. Variable speed control can help in some applications, but it is not automatically the best answer. If demand is steady and the system is simple, a fixed speed setup may be more cost-effective and easier to service.
Think about system design, not just the pump
A bore pump does not work alone. The controller, pressure switch, dry run protection, level sensors, non-return valves and storage arrangement all affect reliability. A well-sized pump in a poorly designed system will still cause problems.
Dry run protection is particularly important where bore yield is variable or seasonal. Water table changes, heavy summer demand and drought conditions can all alter how the bore behaves. Pump protection should reflect that reality. For lower-yielding bores, staged pumping into storage is often safer than direct high-demand supply.
If solar is part of the plan, sizing becomes more application-specific again. Solar bore pumping can work very well for tanks and stock water, but the available pumping window and variable output need to be factored into daily water demand.
Common sizing mistakes to avoid
The most common mistake is sizing the pump to the bore depth instead of the pumping water level and full delivery head. The second is ignoring sustainable bore yield. The third is treating all applications the same.
A house supply needs different thinking from a tank fill setup. An irrigation line with long pipe runs needs different thinking from a short transfer arrangement. There is also a tendency to overlook future changes. If you are planning more irrigation, additional troughs or a second dwelling later, it may affect how the system should be set up now.
At the same time, planning for future expansion does not always mean buying a much larger pump today. Sometimes the better option is designing the system so it can be upgraded cleanly later, without forcing the current setup to run outside its ideal range.
When to get help with bore pump sizing
If you have reliable bore test data, known drawdown figures and a clear application, sizing can be straightforward. If any of those are uncertain, it is worth getting technical advice before buying. Bore pumps are not the place for guesswork, particularly when access is difficult or downtime affects stock, irrigation or household supply.
This is where a specialist supplier matters. Foundation Pumps works with bore pump applications across domestic, rural, commercial and industrial settings, so the discussion is not limited to catalogue specs. It is about matching the pump, controls and system layout to the way the site actually operates.
The right pump size is the one that delivers the water you need, at the pressure you need, without stressing the bore or the equipment. Get that balance right and the system tends to be quieter, cheaper to run and far more dependable over the long term.
If you are sizing a new bore pump or replacing one that never quite performed properly, start with the real numbers - flow, pumping level, pipe run and outlet pressure. That usually tells a clearer story than the old motor nameplate ever will.