Backflow prevention assemblies can reduce or eliminate backflows by segregating drinking and non-potable water piping. This is done either by providing an air gap or by installing a backflow prevention assembly (BPA) between the two plumbing systems.


Winter Storm Updates

As a result of wide-spread freeze damaged backflow preventers, a supply shortage is being reported. Austin Water Special Services has developed an alternative compliance method.  Plumbers and property owners may install a spool piece until a new backflow preventer can be installed. In order for this method to be in compliance, plumbers and property owners must agree to deactivate the hazards that could potentially backflow and introduce contaminants into the system.  Documented agreement must be submitted. Failure to adhere to this temporary agreement or in the event of a violation to these conditions, plumber or property owner face possible criminal complaint.

Austin Water will update this temporary change once inventory of backflow preventers return to normal levels.  

Backflow Prevention Assembly Types

Air Gap

  • Vertical, physical separation between the end of a water supply outlet and the flood-level rim of a receiving vessel
  • Separation must be at least twice the diameter of the water supply outlet and never less than one inch
  • Effective against backpressure backflow and back-siphonage and may be used to isolate health or non-health hazards. 
Reduced-Pressure Backflow Assembly (RBPA)
  • Includes two independently acting, spring-loaded check valves with a hydraulically operating, mechanically independent, spring-loaded pressure differential relief valve in between
  • Effective against backpressure backflow and back-siphonage and may be used to isolate health or non-health hazards. 
  • Required to be testable
Pressure Vacuum Breaker (PVB)
  • Consists of an independently acting, spring-loaded check valve and an independently acting spring-loaded, air inlet valve.
  • May be used to isolate health or non-health hazards, but is effective against back-siphonage only. 
  • Required to be testable
Double Check Valve Assembly (DCVA)
  • Consists of two independently acting, spring-loaded check valves
  • Effective against backpressure backflow and back-siphonage, but should be used to isolate only non-health hazards
  • Required to be testable



It is important that the backflow prevention assembly match the location’s particular hydraulic conditions and is suitable to protect against the degree of hazard present. Any BPA installed must be a design approved and listed by University of Southern California Foundation for Cross Connection Control and Hydraulic Research (see our Approved Backflow Prevention Assemblies List). Also, the BPA must be installed according to the most recent plumbing code adopted by the City of Austin.

Testing and Maintenance

Once installed, these BPAs are subject to initial and periodic testing and maintenance requirements to confirm their continued operational effectiveness. Such testing must be performed by a state licensed Back-flow Prevention Assemble Tester registered with the City of Austin. Licensing, registration and other tester-specific information is also available online (see Backflow Prevention Assembly Tester Information).