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Selecting the right pump to go with my water tank

Selecting the right pump to go with my water tank

What kind of pump do you require?

It is possible to find a variety of rainwater harvesting pumps with varying features and specifications.

What is the best way to select a water pump? Let us narrow the field.

Rainwater harvesting can be used for the following purposes:

1. Only for use in the garden or outdoors

2. Household-wide

3. Auxiliary water systems (plumbed to toilets, washing machine, garden tap with automatic mains water switching)


Gardening or external use only

A garden pump is usually plumbed to only one tap and is the most affordable pump in the range. With them, you can get water out of a hose at a decent pressure, run a sprinkler system, top up the pool, wash the car, etc.

Garden pumps typically have a maximum flow rate between 40 and 60 litres per minute and a maximum head pressure between 30 and 50 metres.


What's the Difference Between Flow Rates and Maximum Head Pressures?


The flow rate is how much water is pumped over a given period of time. It is measured in Litres Per Minute.

Maximum Head Pressure refers to the total amount of pressure the pump can build up, expressed in metres. In theory, a pump with a maximum head of 38 should shoot water 38 metres through a pipe the same size as the pump's outlet.



Whole of House Pumps

Since they must supply water to many outlets and appliances at once with relatively constant pressure, Whole-of-House pumps tend to have much higher flow rates.

Having multiple impellers in the pump is one way to accomplish this. It's a bit like a circular fan that is designed to throw water in a circular pattern.

The extra impellers work in stages, so one impeller throws water to the next, and so on. These sorts of pumps are called multistage pumps.

The typical multi-stage rainwater harvesting pump will ensure a maximum water flow of around 100 litres per minute with a maximum head of between 30 and 60 metres. 


Pumps with variable speeds and whole-house applications

As the pumps run at variable speeds, the pressure is maintained continually. By turning on multiple taps, for example, inverter technology increases the speed of the pump to maintain pressure as the flow rate increases. The pump uses less electricity, which also results in energy savings.


Support water systems

Tanks installed on new homes with mains water access are usually plumbed to the toilets, washing machine, and at least one outside garden tap. Up to 40% of the water inside a typical home is used to flush toilets and wash clothes.

Although the water tanks are quite small, they can run dry very quickly during dry seasons.

For this reason, pumps with mains water switching devices were developed. The mains water switch prevents the pump from kicking in when the tank runs dry by opening the mains water supply to the toilets and washing machine. Ideally, the system should activate at least once each day to test for water in the tank.


Once you understand the purpose of your rainwater tank and pump - you'll know what kind of pump you need.

In summary:

  • If it's just for the garden, you want a garden pump
  • If it's for the whole house, you want a multi-stage pump
  • If it's for auxiliary (support) water systems that work alongside your mains (town) water, you want a pump with a mains water switching device.

Your final decision is if you are after an external (outside of the water tank) or submersible (inside the water tank, underwater) system. 

But we'll save that for a future post.