Greywater reuse and cross-connection control

Core idea

Greywater is collected wastewater from selected uses and can be treated for suitable non-potable purposes. Its quality varies and it can deteriorate during storage. A reuse system therefore needs controlled collection, treatment, storage, overflow and distribution, with robust separation from wholesome-water pipework.

What to recognise

• Define which sources and end uses the system design permits; kitchen and toilet wastes are not ordinary greywater inputs.
• Provide suitable backflow protection where wholesome water supplies top up the system.
• Identify non-potable outlets and pipework so users and future workers cannot confuse them.
• Prevent cross-connections during installation, alteration and maintenance.
• Route overflow, warning and drain connections to suitable visible or safe positions.

Apply it

Trace both systems from source to outlet. At every interface, ask what happens if a valve passes, a pump stops, a storage level rises or supply pressure falls. Commission by proving identification and separation, not only by showing that a WC cistern fills.

Keep the boundary clear

Reused water is not wholesome because it looks clear. Treatment requirements, permitted uses and maintenance follow the system design and applicable regulations. Do not connect a hose or temporary bypass between systems, and do not assume a single check valve is adequate for the assessed fluid risk.