Rainwater Reuse System – Selecting the Right Pump and Changeover Device

In earlier parts we covered how a changeover device works and how to lay out a compliant system. This section focuses on choosing the right pump and changeover device, as these are central to the performance and reliability of a rainwater reuse system.

Why the Pump Matters

The pump maintains flow and pressure across the fixtures being supplied by rainwater. When the pump is matched properly to the size of the home and usage pattern, the system runs smoothly and reliably.

When selecting a pump, consider:

• Flow rate — must meet fixture demand.
• Head pressure — must be enough to reach all outlets, particularly in multi-storey homes.
• Automatic operation — the pump should operate seamlessly with the changeover device.
• Run-dry protection — essential to prevent pump damage when the tank is empty.
• Noise and location — mount the pump on a stable, dampened base and protect it from weather exposure.

Powered vs Passive Changeover Devices

The changeover device determines how the system switches between tank water and mains supply when the tank runs low.

Powered Changeover Devices

• Use a solenoid valve to control supply.
• Require mains power to operate.
• Deliver reliable switching and stable pressure.
• Do not supply water during a power outage.

Passive (Pressure-Based) Changeover Devices

• Require no power — operate using water pressure.
• Continue to supply mains water during power cuts.
• May provide slightly lower outlet pressure.
• Less suitable for complex or high-demand systems.

Both types provide continuous supply. Choose passive where resilience during outages is important, or powered where consistent pressure is the priority.

Pre-Plumbed Tank and Pump Combos

For domestic homes and small commercial installations, a pre-plumbed pump and changeover system can greatly simplify the installation process.

• The pump and changeover device are factory fitted to the tank.
• Components are tested for correct operation before delivery.
• On-site installation time is reduced.
• Council sign-off is simplified due to consistent configuration and documented specifications.

View configuration options:

Promax Slimline Tank & Pump Combo 2000 L

Full Promax Slimline Tank Range

Choosing the Right Tank Size

If the tank forms part of a compliance requirement (such as SMAF or a dual-purpose detention and retention system), the minimum volume will be set under the resource or building consent.

If the system is being installed voluntarily, tank size can be chosen based on available space, household usage, and sustainability goals.

For guidance on household and seasonal performance, use a tank sizing calculator: Promax Tank Size Calculator

Installation and Best Practice

• Confirm the changeover device includes a built-in dual-check valve for backflow compliance.
• Use lilac non-potable pipework and clear signage.
• Mount the pump in a sheltered position, securely fixed.
• Test system operation by allowing the tank to empty to confirm automatic switching.
• Provide the homeowner with the installation schematic and maintenance instructions.

Why a Pre-Configured Promax System Makes Sense

• Fully tested and matched components
• Automatic mains backup included
• Faster on-site installation
• Council documentation and compliance support
• Reduced installation risk and variability