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Choosing a Water Pump for Your Rainwater Tank

If you want access to your rainwater from different locations around your property, then you will need a water pump. Choosing the right pump might seem like a difficult decision, but this article is intended to give you a better understanding of pumps to help make your decision easier.

Water Pump Considerations

There are a range of features to consider when purchasing a water pump for your tank.
  • Pump noise – if you want your pump to be very quiet, then using a submersible pump might be for you. Unlike external pumps, submersible pumps are placed inside the tank and so the water will muffle their noise.
  • Rain-to-mains switching system – what will happen if you go to access your tank water and it is empty? Being able to switch to your mains water automatically is a good backup solution especially when plumbing your rainwater for toilet and laundry use.
  • Energy usage – is the pump energy efficient?
The main thing tank owners want to know is whether the water pump will be powerful enough to pressurise water to where it is needed. Many of these other factors might impact upon your selection, but at the end of the day ensuring the pump will deliver the right pressure is crucial.

Understanding Water Pressure in Pumps

When considering the pressure requirements of a water pump, you will need to first identify the number of tap locations you wish to access water from. Most pumps have a recommended number of taps they should be good for, how you should also consider the rated head and flow rate. Water pumps will generally have a graph that maps the flow (litres per minute) against the head (metres). You might be interested to read two articles we have describing pump head and pump flow rates, however to summarise each here:
  • Pump head is the distance your pump and pressurise water upwards. If you were to attach vertical pipes to the pump, how far could it pump the water up against gravity? Pumps often detail “Maximum Head” and “Rated Head” values. Understand that at the highest head point the water pressure would be zero and maximum head represents ideal piping conditions. So, you want to pay more attention to “Rated Head” which represents the ideal height you should consider the pumps use for – pumps generally won’t deliver above their rated head.
  • Pump flow rate is the volume of water, litres per minutes (LPM), that a pump can push through pipes. It is important to understand the “Maximum” flow rate is what the pump can pressure immediately from itself. The real flow rate however will be influenced by distance to access points, pipework bends and elevation. The “Rated” flow rate is what the pump is designed to operate for.
With a better understanding of head and flow rates, how do you decide if a pump is right for you? First, you should consider your real-life use. Standard shower heads and taps use about 15-25 litres of water per minute, while water efficient heads use less than 10 litres per minute. This means more “mileage” (more efficient pressure use) can be had from a water pump by installing water efficient taps, heads and nozzles. Also keep in mind that not every tap or access point is going to be running at the same time – aim for a typical maximum flow rate based upon real life use. Second, you should look at the flow rate chart of the pump being considered. For example:
Choosing a Water Pump for your Rainwater Tank
Figure 1 Reefe Pump Chart
  If the pump needs to pressurise water to a head level above the “Rated Head”, then look for a more powerful pump. Ideally, you want to be able to achieve the “Rated Flow Rate” – if the rated flow rate on a pump seems too small, then it would be safer to opt for a more powerful pump. You should select a pump where your desired flow rate is below the head necessary. Some pump brands are more reliable and have systems installed to help with a more consistent water pressure. National Poly Industries sell a range of high-quality pump brands, and can help advise you on the best fit for your water tank. If you need help choosing the right tank pump for your home water tank, contact our expert team for advice today.