Choosing a borehole pump comes down to two numbers: how much water you need (flow) and how high it must be lifted, including pipe losses (total head). Get those right and the pump will run for years. Get them wrong and it will run dry, pump sand or never fill the tank. This guide shows you how to work it out in five steps, with a worked example.
Short on time? Use our Pump Finder – enter your borehole details and it shows the pumps whose curves meet your duty – or WhatsApp us the numbers and we will size it for you.
Step 1: Know your borehole
You will find most of this on the drilling or yield-test certificate:
- Diameter (casing size) – a 4″ pump needs a casing of at least about 100 mm inside diameter; 6″ pumps need 150 mm or more. 3″ pumps are for narrow boreholes.
- Depth – the total depth of the hole.
- Static water level – the depth to the water when nothing is pumping.
- Yield – how many litres per hour the borehole can deliver continuously, and the dynamic (pumping) water level at that rate.
The pump is normally installed well below the dynamic water level but a few metres above the bottom of the hole, so it stays submerged and doesn’t suck up sand.
Step 2: Decide how much water you need
A household typically needs about 1 000–2 000 litres per hour (1–2 m³/h) to fill a tank in reasonable time. Irrigation, livestock and small holdings need more. The golden rule: never pump more than the borehole can supply – choose a flow of no more than about 80% of the tested yield. A pump that out-pumps the borehole will run dry and burn out.
Step 3: Work out the total head
Total head (m) = dynamic water level + height to the tank inlet + pipe friction + pressure needed at the outlet (1 bar ≈ 10.2 m)Note that the lift starts at the water level while pumping, not at the pump depth. The pump depth only matters for the length of pipe (friction) and for keeping the pump submerged.
Friction depends on the flow and the pipe size. Approximate losses in HDPE pipe, metres of head per 100 m of pipe:
| Flow | 25 mm | 32 mm | 40 mm | 50 mm |
|---|---|---|---|---|
| 1 m³/h (17 L/min) | 4 m | 1.2 m | 0.4 m | 0.1 m |
| 2 m³/h (33 L/min) | 15 m | 4.5 m | 1.5 m | 0.5 m |
| 3 m³/h (50 L/min) | 32 m | 9.4 m | 3.2 m | 1.1 m |
| 4 m³/h (67 L/min) | 54 m | 16 m | 5.4 m | 1.8 m |
| 6 m³/h (100 L/min) | – | 34 m | 11.5 m | 3.8 m |
Add about 10% for bends, valves and fittings. If the friction is more than a few metres, the next pipe size up usually pays for itself in a smaller pump and lower electricity bills.
Worked example
- 4″ borehole, 80 m deep, yield 3 000 L/h, dynamic water level 40 m; pump installed at 55 m
- Tank on a stand, inlet 8 m above the ground, 40 m from the borehole
- 32 mm HDPE pipe; wanted flow 2 m³/h (2 000 L/h – below 80% of the yield)
Pipe length ≈ 55 m (down the hole) + 40 m (across) + 8 m (up) ≈ 103 m. Friction at 2 m³/h in 32 mm ≈ 4.5 m per 100 m → about 4.6 m, plus 10% for fittings ≈ 5 m.
Total head ≈ 40 m + 8 m + 5 m = 53 m at 2 m³/hNow look for a pump whose curve delivers at least 53 m at 2 m³/h, with a little margin. For example the 4SD3/10 (0.55 kW) delivers about 62 m at 2 m³/h according to its curve – enough, without being oversized. Every pump on our site with a published curve has a “Check your duty point” tool on its product page: type in your flow and head and it tells you instantly if the pump can do it.
Don’t be tempted by the “max head” in a pump’s name. Maximum head is at zero flow. What matters is the head the pump delivers at the flow you need – that is what the curve shows.
Step 4: Choose the motor and power supply
- 220 V single-phase motors are common up to about 2.2 kW on 4″ pumps. They need a control box (with the start capacitor) or a controller.
- 380 V three-phase for bigger pumps and 6″–10″ boreholes.
- Solar – solar borehole kits pump during the day straight from the panels, ideal for farms and load-shedding. Size the tank to store a day’s water.
- Cable – the drop cable must be sized for the motor current and the depth, or the motor will see low voltage and run hot. Ask us if you are unsure.
Step 5: Protect the pump
- Dry-run protection – an intelligent controller switches the pump off when the water runs out and restarts it later. It is the cheapest insurance a borehole pump can have.
- Tank level control – a float switch or probes stop the pump when the tank is full.
- Surge protection – boreholes are lightning magnets; a surge arrestor protects the motor and controller.
- Pumping straight into the house? You need a pressure system – a pressure tank and pressure switch, or a VSD controller that keeps the pressure constant.
Common mistakes
- Buying on “max head” instead of the head at the required flow.
- Pumping more than the borehole yields – the pump runs dry, sucks sand and fails early.
- Forgetting the tank-stand height or using pipe that is too small.
- No dry-run or surge protection.
Let us size it for you
Send us your borehole depth, water level, yield, tank height, distance and pipe size – we will recommend a pump, motor and controller that match.