Choosing a water pump for irrigation: flow, head and power explained
A pump that is too small will not deliver water where you need it; one that is too big wastes fuel or electricity. Two numbers — flow and head — decide the right choice.
Flow: how much water you need
Flow is the amount of water the pump delivers, usually in litres per minute or per hour. Work out how much your crop, tank or sprinklers need in a given time, and choose a pump that can supply it.
Head: how high and how far
Head is the total effort the pump must make. Add together the height the water must be lifted, the depth it is drawn from, and an allowance for the friction in long or narrow pipes. The longer the pipe and the more bends, the more head you need.
- Lift from the water level up to the pump (suction)
- Height from the pump up to where the water is delivered
- Friction loss in the pipe and fittings
Match them to a pump
Every pump delivers less water as the head increases. Check the pump’s performance information for the flow it gives at your total head, not just its maximum flow.
Electric or petrol?
- Electric pumps are quiet and economical where there is a reliable supply
- Petrol-engine pumps are portable and work where there is no power, such as remote fields
Practical tips
- Use pipes wide enough for the flow — narrow pipes cost you head
- Fit a strainer or foot valve on the suction side to keep out dirt
- Never let a pump run dry — it can overheat and damage the seals
- For deep wells, a submersible pump is usually the right choice rather than a surface pump