September 6, 2023

Guide to Water Pump Selection

Water pumps are an essential component in rainwater harvesting systems for domestic homes and irrigation. They are responsible for pushing or pulling the flow of water to transfer water from tank to outlets and appliances in the home and garden. Selecting the best water pump solution for your needs is vital to ensure you have the right pump for the job at hand.

A bit about rainwater harvesting systems: they enable the collection and utilisation of rainwater from rooftops and other solid surfaces on a property. Harnessing this abundant resource gives you complete control over your own personal water supply whilst reducing reliance on mains water. A 2014 study by the CSIRO found that 96% of properties found their rainwater harvesting system to be beneficial, collecting an average of 42,000L each year. Cost-saving is but a small part of the value offered through rainwater harvesting, as you will be unrestricted in the use of your environmentally friendly rainwater reserves regardless of shortages or restrictions on mains water supplies.

Here are the main factors to consider when purchasing a water pump for your rainwater harvesting system:

  • Type of pump – submerged or free-standing
  • Size of pump – Determined by the application and the size of the tank and dwelling
  • Water quality – Potable water, grey water or dirty water
  • Accessories

In this article, we’ll explore what you need to consider before buying a pump for your rainwater tank or rainwater harvesting system.

Types of Pumps – Submersible and Jet Pumps

There are two common variations when it comes to pumps for rainwater harvesting systems – submerged (known as submersible pumps) and free-standing pumps such as jet pumps.

A submersible pump can be fitted in the rainwater tank, saving space and emits much less pump noise.

A free-standing pump is often the more affordable option and will be available in a wider range of pumping capacities. Free-standing pumps include jet pumps and multi-stage jet pumps which can also be purchased in kits with a pressure controller and a weatherproofing cover.

However, this type of pump requires weatherproof housing or and a protected spot near to the tank.

Submersible Pump Jet Pump
Location Installed inside the rainwater tank, typically submerged in the water. Located outside the tank, usually at ground level or above.
How it Works Uses an impeller to directly push water out of the tank. Uses a suction pipe and impeller to draw water from the tank
Pros and Cons Provides quieter operation since it’s submerged.
Requires less maintenance as it is protected from external elements.
Does not require priming.
Ideal for deeper tanks.
Tends to be noisier due to its external placement.
Requires weatherproofing.


Bromic Waterboy offers a range of submersible pumps and jet pumps to suit a variety of different recommendations. Waterboy Rains to Mains Pumps and Pump and Controller Kits are specifically curated for use with rainwater harvesting systems, including pressure or switch controllers for a complete pump set-up.

Consult with your plumber, pump supplier or hydraulic consultant for help on selecting the right pump.


How to Size a Pump

To help your plumber size the correct water pump, you’ll need to consider the size of your dwelling and number of applications. For example, a double-storey home will need a higher pressure/head.

To choose the right water pump, you’ll need to consider a few important factors:

  • Required flow rate – The measurement of how many litres can be pumped per minute
  • Suction head – Total height or vertical distance pumped from the water source to the pump
  • Required total head lift – Total height from the water source to the final destination
  • Required pressure – Pressure for water can be calculated using P(kPa)=9.81xhead(m)
  • Inlet and outlet– The size and type of the inlet should fit the hose or piping to be attached

To determine the requirements of your pump, you’ll need to understand how your pump will be used – including the number of appliances, the size of your tank and the length and size of pipework.

The Size of the Dwelling

A double-storey home with multiple appliances for example, will require a higher total head lift and pressure than a single-storey home with less appliances. For this type of dwelling, you’ll want to consider a larger pump.

You’ll require a larger water pump based on the size of your dwelling and number of applications. Consult with your local plumber to determine the right size for your home and application.

Required Flow Rate

To understand the volume of water required within the dwelling that is running the water pump, you will have to work out the number of taps or outlets, both inside and outside, that are likely to be in use simultaneously. Keep in mind that different outlets will have different flow rates.
To work out your household water flow rate you should check the specifications of the specific tap/appliance. There is also the below table from AS/NZS 3500 – Australian National Plumbing and Drainage Part 1 – Water Supply that can provide guidance on the approximate flow rates.

Flow Rates at Fixtures or Appliances

The flow rates to fixtures, appliances, taps, valves and cisterns shall be not less than the flow rates specified below. The maximum flow rate from a shower, basin and kitchen sink or laundry trough outlet shall not exceed 9 L/min

Fixture / Appliance Flow Rate L/min
Water Closet 6
Bath 18
Basin 6
Spray Tap 1.8
Shower 6
Sink (standard tap) 7
Sink (aerated tap) 6
Laundry Tub 7
Washing Machine 12
Hot Water System 12
Hose Tap (DN20) 18
Hose Tap (DN15) 12


Water Quality

To select the best water pump for your needs, you must identify the type of water you will be dealing with. The pump you select must be suitable for use with the water type application.  The 3 key types are outlined below:

  • Potable water (drinking water) is water that is safe to drink or to use for food preparation. In Australia, the mains water is classified as potable ater. When collection rainwater for drinking, it is important to follow the requirements and hygiene practices to prevent harmful contamination. Pumps and filters that are used for potable water should be AS/NZS4020 approved
  • Greywater is typically water from rain collected off roofs as well as re-usable wastewater from washing machines, showers and other sources. Greywater replaces the need to use mains water for watering gardens or lawns and can potentially save thousands of litres of drinking water.
  • Dirty Water is typically water that contains small particles. Used for watering gardens or lawns which can potentially save thousands of litres of drinking water. Includes rain or greywater.



Water pumps can be supplied with accessories for a complete and weatherproof package. If you choose to install a jet pump, we recommend installing a controller and also a weatherproofing cover to reduce contact with the elements.

Pressure Controller

This unit is an pump controller that automatically turns on after a pressure drop at the pump outlet (opening taps) and stops water flow when the tap is turned off.. The Bromic Pressure Controller offers a great economic solution for electric pumps.

Mains Switch-Over Controller

A Automatic water pump pressure switch is used in residential water systems to switch between tank water and mains water. The Waterboy Wizard Controller offers a patented solution to water changeover. We suggest also looking for a pump cover that can protect a switch controller against the elements. Often controllers and pumps are available in convenient kits. For extra protection against the elements, we recommend the Waterboy Wizard Pro Pump Controller Kit  or a Pump and Controller Kit with a controller cover included.

Controller Pump Covers (or ‘Housing’)

This is an automatic pressure switch solution within a weatherproof UV protective housing.

Bromic Waterboy™ Pump Solutions

Bromic Waterboy™ offers pump system solutions for rainwater harvesting including submersible pumps and external pump options to fulfil the needs of all rainwater harvesting systems, big or small.

The Waterboy™ Rains to Mains Pumps and Pump & Controller Kits are specifically designed as complete solutions for pain-free installation and are both backed by Bromic’s industry-leading in-field warranty, with our team of skilled technicians standing by should the unthinkable happen.


Bromic Plumbing & Gas