Does my irrigation system need backflow protection?

Irrigation sits in soil, and soil contains everything from fertiliser and manure to whatever the dog contributed. If the mains pressure drops, water can be drawn back through the system into the drinking supply. That is why every water authority treats irrigation as a hazard rather than as an ordinary outlet.

What is usually required

• A backflow prevention device matched to the hazard rating, which rises if fertiliser injection is involved.
• Installation by a licensed plumber, since it is a connection to the water service.
• Annual testing by a person with a backflow endorsement, where the device is a testable type, with results lodged with the water authority.
• Registration of the device with the water authority in many areas.

Things that catch people out

• Buying the property with an existing system and inheriting an untested device and an unregistered one.
• A hose end connected to a fertiliser applicator, which is a hazard even without a fixed system.
• Extending an existing system past the point the original device was sized for.
• Connecting an irrigation system to a rainwater tank with a mains top up, which creates a second cross-connection risk.