Rainwater Harvesting Pump Guide

For those who only want to water a small garden then fittings to the gutter, a water tank, a hose connector at the bottom of the tank, overflow to your stormwater pipe and a hose is about all you need as long as your garden isint higher than the tanks water level.

On the other end of the scale, there are those who want to water their larger gardens and lawns, wash their cars as well as use the tank water to flush the toilets, wash the clothes in the washing machine and top up the pool or water feature.

The ideal system set up uses a automatic pump and switch system (ie. :-Davey Rainbank, Onga Waterswich, Grundfos Rainswitch, Bianco Rainsaver) which uses tank water, until the water gets below a certain level and then automatically switches the system over to mains water. Having a automatic pumps system like this can save you alot of money by having your tank and pump connected to your toilets and your washing machine, both of which use a lot of water in every household.

Table 1 : Benefits of Pumping Systems


External Pump

In-tank Pump


Correctly installed will provide consistent performance.  Long or poorly installed suction lines  can cause problems

Correctly installed will provide consistent performance


Horizontal Multistage design pumps are extremely quiet but lower cost jet pumps can be noisy

Water in tank will minimise noise

Electrical cabling

Can be an issue for children and animals

Less accessible if installed correctly.

Weather protection

Needs to be protected from sun and rain

No protection required for the pump but may need protection for external controller (from sun and rain).


Easier to maintain

Need to pull pump out of tank to maintain


Usually lower cost

Can be higher cost


Water Security – Mains Switching Devices and Top-up Systems

A pumping system can be used for garden watering and general outside use through a standard garden tap. If the pumping system is required for water use to inside the house (toilets, washing machine or whole of house), and mains water is available, then an automatic tank connection device is recommended to ensure that the appliances will work even when the rainwater tank has run out of water.

There are two types of automatic tank connection devices:

1) Mains Switching System (either electronic or hydraulic),

An Automatic Mains Switching System  will change to mains water supply when there is no water in the rainwater tank. It will revert from the mains water supply back to rainwater when it rains and the tank has water.

Diagram 1 – Mains switching system for inside house supply

2) Top-up system.

A Tank top-up device will always keep a certain level of water in the rainwater tank so the pumping system is always in operation.

These two systems are shown in Diagram 2. The Characteristics of these systems are summarised in Table 2.

Diagram 2 – Top up system for inside house supply


Table 2 – Characteristics of Mains Back-up Systems


Auto Mains Switching System


Tank Top-up





Requires a pump to provide water




When the pump does not work an AMSS auto switches to mains. A TTU does not.

Requires electric power to provide water




When there is no electricity an AMSS auto switches to mains. A TTU does not.

Requires electronic switches to operate


Not for mains /rainwater switching function but usually  requires an electronic controller to operate pump

Not for rainwater filling of tank but usually  requires an electronic controller to operate pump

A TTU and hydraulic AMSS use mechanical devices only for switching of tank filling but the pump does require a controller – usually electronic.

Requires Mains water flow


Normally full mains flow and pressure

Yes Dependent on system whether full flow and pressure


Reliant on pump to provide flow and pressure

Some hydraulic AMSS use pressure reducing devices that can reduce flow and pressure.


Problem Trouble-shooting

It is important that the operation of the pumping system is understood in order to maintain the system and fix problems. If there is a problem with the pumping system then refer to the Operations Manual of the pump and/or mains back-up system.

The table below provide generic troubleshooting, which may or may not apply to a specific model or brand of system:


Table 3 – Trouble shooting guide for pump systems


Root Cause

Possible Solution

Pump is turning on and off repeatedly

The pump will turn on when the pressure in the discharge piping is low. It will turn off when it has pumped the pressure high. The pressure in the household piping can only go down if there is a tap open or a leak in the system

Check all taps for leaks. Check all toilets that there is no slow leak into the bowl. Check washing machine by turning off water isolation tap. Repair leaks if necessary. If leak cannot be found contact a plumber to investigate leak that may not be visible.

Pump continually operates

The pump will operate continually if there is a tap open or a severe leak. If this is not the case then the pump controller may be faulty.

Check for open tap and leaks in system from toilet and pipework. Contact a plumber if there is a leak. If no leak is detected, contact the pump manufacturer, repairer, or retailer.

Pump doesn’t operate when rainwater in tank

The pump should operate when a tap is opened or a toilet is flushed. There could be electrical supply problems to the pump or even pump failure.

Turn the pump off and then on at the power point.

a) If the pump does not start, test power point by using another appliance. If other appliance doesn’t operate, check circuit breaker at switchboard. Reset circuit breaker and test appliance again. If circuit breaker trips again contact electrician. If pump is causing circuit breaker to trip contact pump manufacturer or retailer.

b) If the pump starts but doesn’t continue the problem maybe with the switching device. Contact the pump manufacturer, repairer, or retailer.

No water to tap or toilets or washing machine

Tank top-up systems rely fully on the pump to deliver water to toilets and/or washing machine. Systems that have electronic or hydraulic switching to mains water should deliver water at all times even when there is no rainwater in tank.

Check pump operation and power supply by following procedure in section above.

Clean all filters and strainers to ensure there are no blockages.

Contact the pump manufacturer, repairer or retailer.

Low flow to tap or toilet or washing machine

There could be blockages in the system that is restricting flow.

It is possible that the pumping system or mains switching system supply is designed for low flow.

Clean all filters and strainers to ensure there are no blockages.

If the flow is still not acceptable contact the pump manufacturer, repairer, or retailer.


Suction Pipe Trouble-shooting

Experience has shown that suction lines cause problems with pumping systems.

The most common cause of suction related system problems is air leaks on suction pipework.  All threads should be sealed with thread tape correctly. (This may involve up to 10 wraps of tape around each thread).

Since tanks, pumps and homes can move over time due to seasonal changes, the use of flexible pipework between all components, especially on the suction can alleviate stress placed on them.

Refer to the diagram below for assistance in overcoming problems caused by suction lines (Diagram 3).

Diagram 3.1 – Long Suction Pipework : Suction pipework that passes under pathways or travels long distances can cause priming problems with pump. Priming problems is caused by air becoming trapped in the pipe and preventing the pump from working.  It is ideal to keep the suction pipework as short as possible. Some pump manufacturers suggest installing a filter or strainer  to protect the pump – check to see if the brand or model involved needs a strainer and where this should be installed.


Diagram 3.2 – Elbows in Suction Pipework : It is better to reduce the number of elbows in the suction pipework where possible. It is best to have no elbows but where necessary have as few as possible. Try to prevent having an elbow directly onto the inlet of the pump. This can cause suction and noise issues with the pump.


Note Y Strainer not required for all models

Diagram 3.3 – Flexible Suction Pipework : It is important to keep the suction pipework short and straight as possible, with a filter or strainer.  If the flexible suction pipework needs to be looped ensure the loop goes downwards. This will prevent air from being trapped in the high point.

Note Y Strainer not required for all models


If you are going with this popular cost saving automatic pump set up to connect your home from tank / mains to the toilet or washing wachine etc, you will need a licensed plumber to do the work.

If still in doubt contact us here , and we can recommend the most suitable pump for your application.