Choose a backflow preventer only after an appropriately licensed and accredited backflow plumber has assessed the connection’s hazard rating, purpose and water-supplier requirements. Do not select one from pipe size or the existing device alone. Understanding how drinking-water backflow is prevented explains why the hazard assessment comes first.
Match the device to the assessed hazard
The hazard rating reflects the potential consequence if contaminated water enters the drinking-water supply:
| Hazard rating | Potential consequence | Common containment option* |
|---|---|---|
| Low | No health risk, but water quality may be affected | An integral meter device or another approved non-testable device |
| Medium | A non-lethal health risk | A testable double check valve assembly |
| High | A potentially lethal or serious health risk | A reduced pressure zone device, air gap or break tank |
*These are indicative options, not a selection guide. The approved device depends on the site assessment, connection details and the water supplier’s current requirements. An unknown or unassessed hazard may need high-hazard protection until it is properly classified.
Assess each connection separately
Connection purpose can change the required protection. Drinking-water, fire-service, standpipe and other dedicated connections should each be assessed; they may not use the same assembly. For example, an approved double check detector assembly may be required for some fire-service connections.
The assessor should consider:
- property activities and possible contaminants
- substances, equipment and processes connected to the supply
- meter size and connection configuration
- the purpose of each separate supply
- current water-authority requirements and applicable plumbing rules.
A change in property use or on-site activities can alter the hazard rating and require reassessment.
Confirm the current requirements
For a property in Sydney Water’s service area, check Sydney Water’s current backflow prevention guidance and have the proposed device confirmed before installation. Requirements for low-hazard meter protection, fire services and other connections can vary with the meter and connection details.
Outside Sydney Water’s area, contact the relevant local water supplier rather than assuming Sydney Water or council requirements apply. Device selection and plumbing work must also comply with the plumbing requirements currently adopted in NSW, including applicable provisions of AS/NZS 3500.1. Owners of testable devices should also check who can install or test a backflow preventer and when testing is required.
You may identify connections and explain site activities, but do not install, alter or bypass a backflow prevention device yourself. This is regulated plumbing work involving the drinking-water supply. Contact our accredited backflow prevention plumbers to assess the connection and confirm whether appropriately accredited personnel are required for specification, installation, commissioning or testing.