Understanding Backflow Prevention Programs

TVWDThe Federal Clean Water Act and Oregon Administrative Rules Chapter 333-61-070 require that Tualatin Valley Water District (and all water purveyors) protect our potable water supplies from contamination by an outside source, through implementation of a Backflow Prevention Program. These requirements try to minimizes the possibility for the water using public to inadvertently contaminate or pollute the public water supply.

This program requires the installation of a backflow prevention device in the plumbing system where the possibility of a cross connections may take place. A cross connection. is an arrangement of piping or faucets which might allow the potable water supply to come into contact with a contaminant. An example of a potential cross connection is a lawn irrigation systems, where fertilizers, chemicals or other contaminants can come into contact with the potable water supply through the irrigation heads.

There Are Four Basic Types Of Backflow Prevention Assemblies:

Atmospheric Vacuum Breaker (AVB)avb

  • One AVB required for each irrigation zone; no control valves (on/off) valves allowed downstream of (after) an AVB
  • Each AVB must be installed a minimum of six inches (6″) above the highest point of water in the zone it serves
  • No chemicals or fertilizers may be introduced into an irrigation system equipped with AVBs
  • No pumps or back pressure on downstream side of (after) an AVB

Double Check Valve Assembly (DCVA)dcv

  • The most common type of backflow device
  • Only one DCVA required to serve the whole system; control valves can be located downstream of the DCVA
  • DCVA must be tested by a state-certified backflow assembly tester when installed, annually or when moved or repaired
  • No chemicals or fertilizers may be introduced into an irrigation system containing DCVAs

Pressure Vacuum Breaker Assembly (PVB)pvb

  • Only one PVB required to serve the whole system; control valves can be located downstream of (after) the PVB
  • PVBs must be installed a minimum of one foot (12″) above the highest point of water they serve
  • PVBs must be tested by a state-certified backflow assembly tester when installed, annually or when moved or repaired
  • No chemicals or fertilizers may be introduced into an irrigation system containing DCVAs
  • No pumps or back pressure on downstream side of (after) a PBV

Reduced Pressure Backflow Assembly (RPBA)rpba

  • Only one RPBA required to serve the whole system; control valves can be located downstream of (after) the RPBA
  • RPBAs must be installed a minimum of one foot (12″) above ground level
  • RPBAs must be tested by a state-certified backflow assembly tester when installed, annually or when moved or repaired
  • In an RPBA equipped system, fertilizer and other agricultural chemicals may be introduced downstream of (after) the RPBA