Backflow prevention rules in WA: when it's required and who's responsible

Backflow prevention isn’t something most homeowners think about until a water authority notice lands in the letterbox or a plumber flags it during other work. It’s a genuinely important piece of infrastructure though, and WA properties with certain connections are required to have it.

What backflow prevention actually protects against

Under normal conditions, water flows one way: from the mains into your property. If pressure in the mains drops suddenly, water can potentially flow backward from your property’s pipes, and if that water has come into contact with a pool, garden chemicals, irrigation systems or other non-potable sources, it risks contaminating the shared drinking water supply. A backflow prevention device is a valve or assembly that allows water to flow in only one direction, stopping that reverse flow before it happens.

When it’s required

Backflow prevention is typically required on properties with a higher contamination risk, which commonly includes:

• Properties with reticulation or irrigation systems connected to the mains supply
• Homes with swimming pools or spas filled from the mains
• Properties with certain commercial or hobby uses involving chemicals or non-potable water sources
• Some properties simply due to their connection type or location in the network

Your water retailer determines whether your specific property requires a device, and at what level of protection, based on the assessed risk. If you’re renovating, adding a pool, or installing reticulation, this is a good point to check whether backflow prevention needs to be added or upgraded.

Testing and ongoing responsibility

Testable backflow devices need periodic testing by a qualified plumber to confirm they’re still working correctly, since a device that’s failed silently offers no protection at all. The property owner is responsible for arranging this testing and for any repairs or replacement if a device fails. Your water authority will typically notify you of the testing schedule that applies to your property and device type. On a rental, that maintenance responsibility follows the same landlord-pays principle covered in our guide to landlord and tenant plumbing responsibilities.

Situation	Backflow risk	Typical requirement
Reticulation or irrigation connected to mains	Higher	Device usually required
Pool or spa filled from mains	Higher	Device often required
Standard residential connection, no special fixtures	Lower	May not be required
Certain commercial or hobby chemical use	Higher	Device usually required

How the device is fitted

Installation is generally straightforward for a licensed plumber: the device is fitted at the point of highest risk, commonly near the water meter, at the boundary connection, or immediately before a specific fixture like a pool fill or reticulation controller. The plumber selects the assembly type based on the level of contamination risk your property presents, since a simple check valve suits a lower-risk situation while a higher-risk connection, such as an irrigation system using recycled or bore water alongside mains, typically needs a stronger assembly like a reduced pressure zone device.

What happens if a device fails or isn’t maintained

A backflow device that fails silently offers no protection at all, which is why testable devices are checked periodically rather than installed and forgotten. If a test finds a device isn’t sealing properly, it needs prompt repair or replacement, since a failed device leaves the shared water supply exposed to exactly the contamination risk it was installed to prevent. Water authorities take non-compliance seriously given the public health stakes involved, so keeping on top of test schedules is worth treating as routine maintenance rather than an optional extra.

What to do if you’re not sure

A licensed plumber can assess your property’s connections and confirm whether a backflow prevention device is required, whether an existing one needs upgrading, and what testing schedule applies. This is worth sorting out proactively rather than waiting for a compliance notice, particularly if you’re planning renovation work that touches your water connections.

This is general information about how backflow prevention typically works in WA, not a substitute for advice from your water retailer or a licensed plumber about your specific property.

To find a licensed plumber who can assess your property, our plumber category ranks Perth operators using our published scoring methodology, and the full directory covers other trades if your project needs more than one.