When shopping for a water pump, one of the biggest challenges customers face is making sense of the technical specifications. Terms like flow rate, head height, pressure, and power often appear in product descriptions—but what do they actually mean, and how do they affect performance? This guide breaks it down in simple terms so you can choose the right pump for your needs.
1. Flow Rate (Litres per Minute or L/min)
The flow rate tells you how much water the pump can move in a given time. It’s usually measured in litres per minute (L/min) or sometimes litres per second.
- High flow rate = moves water quickly, good for filling tanks or transferring water.
- Low flow rate = delivers smaller volumes but often at higher pressure, good for household taps or irrigation.
Max Flow vs Rated Flow:
- Max Flow is the highest volume of water a pump can move, usually measured when there is almost no resistance (very low head). It’s a “best case” figure.
- Rated Flow is the realistic flow the pump can deliver in normal working conditions. This is the number you should focus on when comparing pumps.
Example: A pump may have a max flow of 120 L/min, but its rated flow at usable pressure might be closer to 70 L/min.
2. Head Height (Metres)
The head height (or simply head) refers to how high the pump can push water vertically. Think of it as the maximum height the water could be lifted.
- Total Head Height: the maximum lift the pump can achieve under ideal conditions (usually at zero flow).
- Operating Head: the real-world height at which the pump can deliver useful flow.
Max Head vs Rated Head:
- Max Head is the highest point the pump could theoretically push water—but at this point, the flow will be close to zero.
- Rated Head is the head height at which the pump delivers a reliable, usable flow. This figure gives a better picture of real-world performance.
Example: If a pump has a max head of 40 metres, it can technically push water that high, but it won’t deliver usable flow at that height. Its rated head may be 25 metres, meaning it performs strongly up to that point.
3. Pressure (kPa or bar)
Pressure is directly related to head height. In fact, 10 metres of head is roughly equal to 100 kPa (or 1 bar) of pressure.
- Higher pressure = stronger water output, good for showers, sprinklers, or firefighting.
- Lower pressure = fine for filling tanks or slow irrigation.
Example: A household with a rainwater pump supplying taps and a shower would typically want around 200–300 kPa (20–30 metres head) for comfortable use.
4. Power (Watts or Horsepower)
The power rating tells you how much energy the pump motor consumes, usually listed in watts (W) or horsepower (HP).
- More power doesn’t always mean better—it depends on the efficiency of the pump design.
- A larger motor is often required for higher head heights or larger flow rates.
Example: A 750W (1 HP) pump may be sufficient for most domestic water supply applications, while a farm irrigation pump might require 2,000W (3 HP) or more.
Putting It All Together
When choosing a pump, you need to balance all four factors:
- Flow rate: How much water do you need at once? Look at the rated flow, not just the max.
- Head height: How far (and high) does the water need to travel? Focus on the rated head for realistic performance.
- Pressure: Do you need strong spray or just steady filling?
- Power: Is the pump powerful enough for the job without being oversized?
Tip: Manufacturers often provide a pump performance curve—a graph that shows how flow rate decreases as head height increases. It also makes clear the difference between max and rated specifications.
Final Thoughts
Understanding pump specifications doesn’t have to be complicated. By knowing what flow, head, pressure, and power mean—and the difference between max and rated values—you can confidently select the right pump for your household, garden, farm, or business.
If you’re still unsure, check the performance curve or ask our team at Water Pumps Direct for advice. We’ll help you match the right REEFE or White International pump to your exact needs.