What backflow preventer means
A backflow preventer is a valve assembly that stops water from flowing backward from a hose, irrigation system or boiler into the drinking water supply.
Where it matters on a plumbing job
Irrigation systems and boilers usually need one, and many water districts require yearly testing by a certified tester. Testing is recurring work that fits a reminder schedule.
What the model code says
- The code defines a backflow preventer as an assembly, device or other means to prevent backflow into the potable water supply. (IRC 2021, Chapter 2)
- Backsiphonage is one type of backflow, the flow of water into the potable supply from any source other than its intended one. (IRC 2021, Chapter 2)
Check which code edition your building department enforces for backflow preventer before you quote.
What it costs
Jobs that involve backflow preventer are priced in the sprinkler system installation cost guide: about $4,000 typical, usually $2,800 to $5,300. The guide shows its sources and what moves the price.
Work it out
- Cost guide: Sprinkler system installation cost
- Licensing: Plumbing license rules by state
- Tools, templates and guides: Free plumbing resources
Sources: 2021 International Residential Code, Chapter 2, Definitions (ICC). Checked October 9, 2026.