Pumps for rainwater tanks.                                                                                                                          February 2020

How do you access the water stored in a rainwater tank?

A simple rainwater system diverts water from your guttering and stormwater system into a tank. A tap mounted on the tank will supply water under gravity pressure. That is to say that the water will flow out naturally, the pressure determined by the height of water in the tank.

As the water level lowers, so does the pressure. This system is fine for filling buckets or watering cans. You could even connect a garden hose if you are happy for the water to flow without any great pressure.  Gravity pressure is improved if the tank is elevated. On a sloping site, you could mount the tank at a high point on the site. It was common practice on country properties to elevate the tank on a tank stand to increase the pressure.

With the availability of affordable pumps, most tanks are now connected to a pump to provide water under pressure for use around your home – uphill, downhill and over some distance.

So, what types of pumps are available for rainwater systems?

Essentially, jet pumps and submersible pumps.

Jet pumps comprise an electric motor coupled to a pump. They draw water in and pump it out under pressure. They are usually mounted adjacent to the tank though they can be located some distance away for functional or aesthetic reasons. A simple pump is operated manually by turning on the power at the powerpoint.

To automate the system a controller is attached to the pump. This device senses demand, such as when a tap is turned on, activates the pump and provides water to the tap or outlet under pressure. Most controllers feature run dry prevention.

When looking for a pump, consider your application, the required flow rate and head (height to which the pump will lift the water). Jet pumps are affordable, compact, and usually self-priming and can be sized to provide greater flow and head.

It is good practice to mount the pump inside a pump cover. This protects the pump from the elements, extends the life of the pump and improves the appearance of the installation.

Submersible pumps are mounted inside the tank. The surrounding water muffles the motor noise, making them less noticeable than jet pumps. They can operate with a float switch to pump water out when it reaches a certain level (such as in an on-site detention tank) or connected to a controller to supply water on demand. The controller is mounted outside the tank.

Again, you need to consider the application, pressure, and head when sizing the pump. Submersible pumps are slightly more expensive than jet pumps.