A borehole pump is the heart of many African farms. It lifts groundwater to your fields, day after day, season after season. If the pump is too small, your crops stay thirsty in the critical weeks. If it is too big, you waste money twice — once on the machine, and again every month on electricity. This guide shows a simple way to size a farm irrigation borehole pump. You can do a first estimate yourself with a calculator. Then send the numbers to our engineers for a final check.
Why Farms Use Borehole Pumps
Rain is not reliable in most irrigation regions. Rivers and dams can be far from the fields, and surface water is often already claimed by other users. A borehole gives you water where you need it, when you need it.
A submersible borehole pump sits down inside the well, below the water. It pushes water up instead of pulling it. That matters: a surface pump can only suck water from about 7–8 metres down, and it loses prime when the level falls. A submersible pump has no such limit — it works with water levels tens of metres below ground. It does not need priming. It is quiet. It is protected from sun, dust, and theft. That is why submersible borehole pumps are the standard choice for farm irrigation from groundwater.
Our QJ/QJT borehole pump range covers wells from 150 mm to 400 mm diameter — the 150–350 mm sizes cover the common 6–14 inch well range. Flow goes from 5 to 600 m³/h. Head goes from 6 to 600 m. Motor power goes from 3 to 250 kW. A small vegetable plot and a large sprinkler farm can both find a model in the same range. See the full line on our borehole pumps page.
Step 1: Estimate the Flow You Need — Net vs Gross
Flow (m³/h) is the first number. The key is to separate two ideas that are often mixed together:
- Net irrigation requirement — the water the crop actually needs, after subtracting effective rainfall.
- Gross supply requirement — the water the pump must actually deliver, after adding the losses of the irrigation system and the pipes.
The simple field method:
- Find the net crop water need in mm/day for your crop, soil, and season. Your local agronomist or irrigation officer can give this figure.
- Subtract effective rainfall (mm/day). The result is the net irrigation requirement.
- Multiply by the area. Remember: 1 mm over 1 hectare = 10 m³ of water.
- Divide by the irrigation efficiency of your system (no system delivers 100% of the water to the roots), and add any conveyance losses in canals or long pipes. The result is the gross daily volume.
- Divide by your pumping hours per day to get the required flow.
- Expansion margin is a separate decision, not part of the calculation. If you plan to add fields later, state it as its own percentage and tell the engineer — do not hide it inside the efficiency figure.
Worked example, with all assumptions stated:
| Assumption | Value |
|---|---|
| Crop and season | vegetables, hot dry season |
| Net crop water need | 6 mm/day |
| Effective rainfall | 1 mm/day |
| Net irrigation requirement (6 − 1) | 5 mm/day |
| Field area | 10 ha |
| Net daily volume (5 mm × 10 ha × 10 m³) | 500 m³/day |
| Irrigation system | drip, field application efficiency about 90% |
| Gross daily volume (500 ÷ 0.9) | about 556 m³/day |
| Pumping hours per day | 10 h |
| Required flow (556 ÷ 10) | about 56 m³/h |
The 90% here is field application efficiency only — how much of the water reaching the field actually serves the crop. Conveyance losses in the pipeline from well to field are neglected in this example; for long pipelines, our engineers add them separately.
If the same farm planned to add 2 ha next year, that expansion margin would be listed separately — for example +20%, giving about 67 m³/h as a planning figure. Different crops, soils, irrigation schedules, and climates change every number in this table, so treat it as a method, not an answer. Our engineers can run the calculation with you — send your area, crop, and irrigation method through the contact page.
One more check: your borehole must be able to give this flow. The well’s tested yield should be comfortably higher than the pump’s duty flow. If the well yields less than the pump takes, the water level falls, the pump draws air, and the motor suffers. When in doubt, size the pump to the well, not only to the field.
Step 2: Drip or Sprinkler? The Pressure Is Different
Flow is only half of the job. The pump must also push the water with enough pressure at the field. Drip and sprinkler systems need very different pressure:
| System | Typical pressure at the field | Notes |
|---|---|---|
| Drip irrigation | low, about 10–20 m (1–2 bar) | needs good filtration; small pipes; lowest energy cost per hectare |
| Sprinkler / rain gun | higher, about 25–45 m (2.5–4.5 bar) | check your sprinkler nozzle rating; big guns need the most pressure |
| Furrow / open channel | almost zero at the field | the pump only lifts water to the channel |
This field pressure is added to your lift. The total the pump must produce is called Total Dynamic Head (TDH): water level depth + elevation difference + pipe friction + field pressure. Read our guide well depth vs pump head (TDH) for the full calculation, and what size borehole pump do i need for the step-by-step method.
A common mistake is to forget friction. Long delivery pipes, small pipe diameters, and many bends all eat pressure. For long pipe runs, ask us to check the friction loss — a slightly larger pipe can save more energy than it costs.
Step 3: A Worked Selection Example
The following is a separate, independent example — it does not continue the 10 ha calculation above. Take a farm with these conditions:
- Borehole diameter: 250 mm
- Dynamic water level while pumping: 45 m
- Elevation + pipe friction losses: 15 m
- Drip system pressure needed at the field: 15 m
- Required flow: about 75–80 m³/h
TDH = 45 + 15 + 15 = 75 m. We add a small margin and look for a pump with a duty point near 80 m³/h at about 80 m head. From our selection table, a candidate model is:
| Model | Flow | Head | Stages | Motor (YQS) | Max outer diameter | Efficiency | Speed |
|---|---|---|---|---|---|---|---|
| 250QJ80-80/4 | 80 m³/h | 80 m | 4 | 30 kW | 233 mm | 75% | 2875 r/min |
This is a candidate from the model name and design point — the final selection is always confirmed against the actual pump curve and your system conditions by our engineers.
The model name reads like this: 250 = minimum borehole diameter 250 mm; QJ = borehole submersible; 80 = 80 m³/h; 80 = 80 m head; /4 = four stages. The 233 mm maximum outer diameter fits a 250 mm well. The 30 kW motor runs on a standard three-phase supply.
Before installing, three fit checks from the manual: the first impeller must sit at least 3 m below the dynamic water level; the unit should not hang deeper than 70 m below the static level; and the motor bottom must be at least 5 m above the well bottom. Water quality also matters — the pumps are rated for water up to 20 °C, with solids ≤0.01%, pH 6.5–8.5, and chloride ≤400 mg/L. If your water test is outside these limits, ask us about options before ordering.
You can try your own numbers in our pump selector, or read how to choose a borehole pump for the complete checklist.
Power Supply on Your Farm
One more check before you order: your electricity. Our standard borehole pump motors are built for a three-phase 380 V ±5%, 50 Hz ±1% supply. On long rural lines, voltage drop and phase problems are common, and a pump motor running on weak or unbalanced power will overheat and fail early.
Every pump set should have a control panel with short-circuit, phase-loss, and overload protection. Where the supply capacity is limited — for example a small transformer or a diesel generator — reduced-voltage, soft-start, or variable-frequency starting can be used. If your supply is non-standard, note this clearly: our standard QJ/QJT sets are three-phase. The factory can build custom 60 Hz, 220 V, or 660 V motors — but a 220 V build does not automatically mean single phase. If your site has single-phase power only, the workable configuration depends on the model and your supply conditions, so please confirm with our engineers before ordering. We explain the choices in our guide single phase vs three phase borehole pumps.
Get Your Sizing Checked
You now have the key numbers: flow, TDH, borehole diameter, and power supply. Send them to us, and our engineers will confirm the model, the matched cable size, and the control panel. Wrong sizing is the most expensive mistake in irrigation; a ten-minute message can prevent it.
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