Buying the wrong borehole pump is expensive. The pump may not reach your tank. It may run dry and burn the motor. It may be too big and waste power every day. Or it may not even fit inside your well casing. Then you pay again — for a new pump, new cable, and a second installation trip.
The good news: learning how to choose a borehole pump is not difficult. You only need five parameters before you talk to any supplier. This guide explains each one in simple terms. It is written for well drillers, importers, and farm owners who buy pumps for real projects, not for engineers only.
1. Flow Rate — How Much Water Do You Need?
Flow rate is the volume of water the pump delivers per hour. We measure it in cubic meters per hour (m³/h).
Start from your demand, not from the pump catalog. A simple method:
- Estimate how much water you need per day. For example, irrigation for your fields, or daily supply for a village or a camp.
- Decide how many hours per day the pump will run.
- Flow rate = daily demand ÷ pumping hours.
Three warnings before you fix the number:
- Do not oversize. A pump that is much bigger than your need cycles on and off too often. It wastes power and wears out faster. Bigger is not safer.
- Do not undersize. A pump that cannot meet peak demand forces you to run it longer hours, and your tank never really fills in the dry season.
- Check your well’s sustainable yield. The pump cannot give more water than the well itself. Your driller’s pumping test tells you the safe yield. The pump flow must stay at or below that yield — never above it. If pump flow exceeds the yield, the water level falls below the impellers, the pump runs dry, and the water-filled motor can be damaged.
If you have several uses — for example irrigation in the day and village supply in the evening — size the pump for the largest single demand, not for the sum of both, unless they really run at the same time.
Our QJ/QJT borehole pump range covers 5–600 m³/h, so there is a series for a small farm well and for a large municipal project. You can see the full range on our borehole pumps product page.
2. Total Dynamic Head (TDH) — Not the Same as Well Depth
This is a common and costly mistake. A buyer says: “My well is 100 meters deep, so I need a 100-meter head pump.” This is wrong.
The pump does not start lifting from the bottom of the well. It starts from the water level inside the well while pumping (the dynamic water level). And head must also cover:
- the depth from ground to the dynamic water level,
- the height from ground up to your tank or outlet,
- friction losses in the pipes,
- any pressure the water must still have at the outlet.
The sum of these is the Total Dynamic Head (TDH). TDH is the number you give to the pump supplier — never just the well depth.
TDH deserves its own article. Read our step-by-step calculation with a worked example: Well Depth Is Not Pump Head: How to Calculate TDH for a Borehole Pump.
Our QJ/QJT series covers heads from 6 m to 600 m, so even very deep, high-lift projects are in range.
3. Well Casing Diameter — The Pump Must Fit
A borehole pump goes inside the well casing. If the pump body is wider than the casing, nothing else matters — it will not go down.
Measure (or ask your driller for) the inner diameter of your well casing. Then match it to the pump series. Our series cover wells from 150 mm (about 6″) up to 350 mm (about 14″), and the product line as a whole is rated for well diameters from 150 mm to 400 mm:
| Minimum well diameter | Approx. inches | Max. pump unit outer diameter |
|---|---|---|
| 150 mm | 6″ | 143 mm |
| 175 mm | 7″ | 168 mm |
| 200 mm | 8″ | 184 mm |
| 250 mm | 10″ | 233 mm |
| 300 mm | 12″ | 281 mm |
| 350 mm | 14″ | 330 mm |
For a quick model shortlist by well size, see: What Size Borehole Pump Do I Need? (Quick Reference for 150–400 mm Wells).
4. Water Quality — Check the Manual’s Red Lines
Water is not just water. Sand, salt, and acid kill pumps. Before you select a pump, test your well water and compare it with the operating limits in our manual:
| Item | Limit (from our manual) |
|---|---|
| Water temperature | not higher than 20 °C |
| Solid content (by mass) | not more than 0.01% |
| pH | 6.5–8.5 |
| Hydrogen sulfide | not more than 1.5 mg/L |
| Chloride ions | not more than 400 mg/L |
Two points matter especially in Africa:
- High mineral and chloride water is common in many regions. If your water is above any limit in the table, do not guess. Send us the water test report. Suitability and material upgrade options must be confirmed with our engineers.
- Sand content above 0.01% wears impellers fast. If your well produces sand, tell us before ordering.
Also remember: our motors are water-filled. The motor cavity must be filled with distilled or clean water before installation. Never run the motor without water.
5. Power Supply — Match Your Grid
The pump motor must match your local power supply exactly. Check three things:
- Voltage. Our standard motors are 380 V ±5%, three-phase.
- Frequency. Standard is 50 Hz ±1%.
- Available capacity. Larger motors may need reduced-voltage starting, soft starters, or variable frequency drives if your supply is limited.
If your grid is different, we can help. Motors can be customized for 60 Hz, 220 V, or 660 V — for example for 60 Hz countries such as Liberia. If your country uses another voltage, please confirm with our engineers before ordering.
Motor power in this range is 3–250 kW. Every pump must run with a control panel that has short-circuit protection, phase-loss protection, and overload protection — a lost phase on a weak grid can destroy a submersible motor, so do not skip the panel to save cost. Our selection manual lists a matched copper cable cross-section for every model, from 2.5 mm² up to 95 mm², with double cables for large motors. Note that the right cable for your site depends not only on motor power but also on cable length, installation method, and voltage drop — so the final cable specification is confirmed with our engineers against your actual installation depth and routing.
How to Choose a Borehole Pump: Quick Checklist
| # | Parameter | Your value |
|---|---|---|
| 1 | Required flow rate (m³/h) | ___ |
| 2 | Total Dynamic Head (m) — not well depth | ___ |
| 3 | Well casing inner diameter (mm) | ___ |
| 4 | Water test: temperature, chloride, solids, pH | ___ |
| 5 | Power supply: voltage / frequency / phase | ___ |
Get a Selection From Our Engineers
With these five numbers, our engineers can shortlist candidate models quickly. The final model and duty point are always confirmed by our engineers against the pump curve — the checklist gets you to the right candidates, not to an automatic final answer.
Send us your five parameters through our online pump selector or the contact page. Our engineers will reply with candidate models, matched motor power, and a quotation.
Ganquan Pump (Tianjin Ganquan Group) manufactures QJ/QJT borehole submersible pumps in 10 series and more than 800 specifications, for wells from 150 mm to 400 mm, flows of 5–600 m³/h, and heads of 6–600 m. (Elsewhere on this site you will also see a 555-model selection table — that figure counts the model-by-model rows in our 2007 selection manual, while “10 series, 800+ specifications” is the product-line summary from the manual’s overview. The two numbers come from different editions and levels of the same catalog.) The QJ series holds a water-saving product certificate (No. ZSRK-JS1660-001-2025, valid until 2028-01-02) and the factory operates under ISO9001.
— Ganquan Pump Export Team