Backflow Prevention Melbourne

The water supplied to the citizens of Melbourne is amongst the best in the world. But what would happen if that water supply started flowing back the wrong way from the citizens? Below we’ll examine backflow and why prevention is so important.

What is Backflow?

Backflow is a term used in the plumbing world to describe an undesirable flow of water in the reverse direction. The backflow of water can carry contaminants back to the primary water supply system, making the water in it unsafe to drink.

Backflow occurs due to pressure changes in the pipe. This can happen, for instance, when a broken water main is being repaired, the water is turned off, the broken section of pipe is removed, water will gush out of the pipes on either side of the broken section, and a vacuum will be created in the water supply system. Under certain conditions, this draws liquid from a potentially contaminated source back into the drinking water supply. Some examples of cross-connections where a backflow incident can occur are:

  • In metal processing or chemical plants where metals in solutions or chemicals used for production can come into contact with the water supply
  • In market gardens, where chemical injectors, irrigation systems and garden hoses are connected to the water supply 
  • When a hose is left running in a container with chemicals such as fertilisers 
  • Car wash facilities, where there is a connection between the scrubber and rinse cycles 
  • Pipework that allows recycled water to enter the drinking water supply.

A dangerous chemical (or contaminant) may get into the water mains which leads into a nearby property. If this contaminated water is used, the occupants of the property could be seriously or fatally injured.

So, what’s a Backflow Prevention Valve? This is a device that ensures non-potable water doesn’t get back into the main water supply system. Simply put, it’s a device that ensures water flows in one direction.

How Does Backflow Prevention Work?

There a number of types of backflow systems: everything from Dual Check Valves, Air Gap (AG) to Reduced Pressure Zone Device (RPZD).

Dual Check Valves are usually for low hazard situations.


Dual Check Valve backflow system.

Image by

Air Gap backflow systems, as the name suggests, have an air gap between the water supply system and the receiving vessel. The air gap prevents non-potable water from flowing back to the clean water supply system.

Air gap backflow system.

Dual Check Valve backflow system.

Image by

RPZD backflow systems, are for high hazard situations. 

Make sure you hire a Licensed Back Flow Prevention Plumber like O’Shea Plumbing of Mount Waverley for installation, servicing and repair. We will let you know what backflow valve/s are required to be fitted on your property. Backflow devices have to be installed in strategic places for them to work correctly.

Hazard Ratings

Of course, having a device is dependent on having your site assessed so that the property’s hazard rating can be determined.

The internal pipework arrangements and the processes carried out on the site will dictate; the hazard rating for the property, the type of valve/s required to be fitted, and where they need to be fitted.

There are three official hazard ratings:

  1. High – any condition, device or practice which in connection with the water supply system has the potential to cause death.
  2. Medium – any condition, device or practise which in connection with the water supply could endanger health.
  3. Low – any condition, device or practice which in connection with the water supply system would constitute a nuisance but not endanger health or cause injury.

Where Backflow valves are to be fitted is divided into 3 areas:

Individual – This is usually a certain piece of equipment or machine to be protected, so it does not contaminate the rest of the property. i.e. the lunchroom.

Zone – This is a room or area within a property to be protected, so it does not contaminate the rest of the property. i.e. the lunchroom.

Containment – This is where a Backflow Prevention Valve is fitted at the water meter at the property boundary, to prevent water from flowing back into the water main.

Why Do You Need a Backflow Prevention Device?

A qualified licensed plumber can assess the hazard rating of your business process and determine the type of device you need to have.

If you have a cross-connection or an installation on your premises with the potential to cause backflow, and subsequent contamination of the water supply occurs, your company may be exposed to:

  • Injury claims
  • Illness or death of occupants
  • Contamination of products and subsequent exposure to product liability claims
  • Litigation and possibly penalties, as the result of actions brought by the health departments under Occupational Health and Safety legislation
  • Liability for damages caused to others at adjoining premises serviced by the same main water supply as your property.

If you want to know more about device installation, Backflow testing and repair of Backflow Prevention Valves contact O’Shea Plumbing of Mount Waverley Vic, Wantirna Vic, Bentleigh Vic and Bundoora Vic. For reliable plumbers Melbourne locals can rely on, call the team of plumbing experts at O’Shea Plumbing on (03) 9888 2887