FAQ about Backflow and Cross Connection-What the homeowner should know

Why do I need a backflow preventer?

  • to prevent actual or potential cross contamination into the public water system
What is backflow or cross connection?

  • cross connection is any connection or possible connection between the drinking water system and any source of contamination.
  • cross connection can occur due to backpressure of backsiphonage
  • backflow is the reversed flow of contaminated water or other liquids into the drinking water
  • backsiphonage occurs when a partial vacuum causes the water flow to reverse and contaminates are siphoned or sucked into your drinking water.
  • backpressure occurs when contaminants under pressure greater than the pressure in your drinking water system are pushed into your drinking water
What are the most common ways for cross connections to occur in a residential setting?

  • lawn chemicals backflow through the garden hose
  • backsiphonage of "blue water" from a toilet into the water supply
  • backpressure of boiler water into office building water supply
  • backflow from fire sprinkler system
Most common backflow preventers for household use can be found at a local hardware store. Below are some examples of what these devices look like: (#2 is the most common)
Backflow pictures
(1) Reduced pressure principle backflow prevention assembly (RPZ) (2) hose bib vacuum breaker (3) Pipe applied atmospheric vacuum breaker (4) wall hydrant with hose bibb vacuum breaker (5) pressure vacuum breaker (6) double gate -double gate check assembly (7) dual check valve.