Plumbing Layout and Council Compliance | Using Rainwater at Home

Once you understand how the changeover device works, the next question is usually how the system should actually be plumbed, particularly when councils like Auckland Council (SMAF rules) require both stormwater detention and reuse from the same tank.

The good news: whether it’s a SMAF dual-use setup, a simple rain-harvest tank, or a domestic emergency reuse system, the plumbing logic is almost identical. The main differences are in how outlets are controlled and how compliance is documented.

Typical Layout: How It Connects

Roof to tank: roof → leaf guards → first-flush diverter (if fitted) → tank inlet

Tank to house: tank outlet → pump → changeover device → house supply line (toilets, laundry, outdoor taps)

Tank overflow: tank overflow → approved stormwater outfall

Key details:

• Mount the pump at or near the tank outlet.
• The changeover device automatically switches between tank and mains.
• Connect overflow to an approved stormwater disposal point, not to ground soakage unless consent allows.
• Label non-potable outlets “Rainwater, Not for Drinking” and use lilac (purple) pipework for reuse lines.

Typical plumbing schematics are available via our specification tools:

• Slimline Specification Tool
• Underground Tank Installation Tool

For additional regulatory guidance, refer to: Auckland Council

Backflow Prevention: Non-Negotiable

Whenever mains water is connected to non-potable supply, backflow prevention is required under New Zealand regulations.

Promax changeover devices include a dual-check valve that provides suitable protection for low-risk domestic reuse supplying toilets, laundry, and outdoor taps.

Some installers choose an RPZ valve; however, this is typically unnecessary for low-risk domestic applications. Ensure your schematic clearly shows the dual-check configuration.

SMAF-Compliant Dual-Use Systems

In Auckland’s SMAF zones, tanks must deliver both retention for reuse and detention to slow runoff leaving the property.

• The upper portion of the tank (detention volume) drains slowly via a calibrated orifice.
• The lower portion (retention volume) is pumped for reuse.
• The changeover device maintains supply to toilets and laundry when retention water runs out.

To satisfy consent, document:

• Detention and retention volume calculations
• Orifice size and invert level
• Backflow device type
• Lilac pipework and signage
• Manufacturer specifications for tank and pump

A SMAF calculator is available to assist with design inputs. See: Promax SMAF Guidance.

Signage and Maintenance

• Label non-potable outlets and use lilac pipework
• Keep leaf guards and overflow screens clear
• Check the changeover device annually for correct switching
• Clean filters and first-flush diverters, especially after long dry periods

With the right changeover device, lilac header pipework, and documented schematics, you’ll achieve a council-compliant, sustainable, and low-maintenance rainwater reuse system that switches automatically between tank and mains supply.