Do outdoor hose bibbs need a backflow preventer?
Yes — sillcocks, hose bibbs, and wall hydrants must have a vacuum breaker to prevent backflow into the potable supply (IRC P2902.4.3).
The IRC requires every outdoor hose connection — sillcocks, hose bibbs, and wall hydrants — to be protected against backflow by a vacuum breaker. This stops contaminated water (from a hose left in a pool, bucket, or sprayer) from being siphoned back into the drinking-water supply.
Acceptable protection includes an atmospheric-type or pressure-type vacuum breaker, a pressure vacuum breaker assembly, or a permanently attached hose-connection vacuum breaker. Many modern frost-proof sillcocks have an integral breaker built in.
On an existing outdoor faucet, a simple screw-on hose-bibb vacuum breaker satisfies the requirement.
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Need this scoped to your jurisdiction?
Adopted edition and local amendments vary by city and county. Ask Donnie checks your jurisdiction and cites the exact adopted section.
Ask Donnie →General information based on the International Residential Code (a model code). This is AI assistance to verify — not legal advice. Confirm the adopted edition and any local amendments with your local building department (AHJ) and a licensed professional before you build.