What cross connection means
A cross connection is any link between the drinking water system and another piping system or source that could let something flow into the drinking water.
Where it matters on a plumbing job
Hoses in buckets, irrigation without a backflow device and boiler fill lines are classic cross connections. Pointing them out on a service call is part of doing the job right and often leads to a backflow install.
What the model code says
- The code defines a cross connection as any connection between two separate piping systems that allows flow from one to the other. (IRC 2021, Chapter 2)
Check which code edition your building department enforces for cross connection before you quote.
Work it out
- 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.