In plumbing safety, what is required to prevent backflow hazards?

• A. Must have air gap
• B. Must have backflow preventer
• C. Must have a trap
• D. Must have venting

Answer: (A)

Backflow hazards are prevented by creating a physical separation between the potable water supply and any potential source of contaminated water. An air gap does this by keeping the water outlet physically disconnected from the drainage path, so no matter how pressure changes, there’s no route for water to flow backward into the clean supply. This simple, fail-safe separation is why air gaps are a primary and widely required method for preventing backflow in many plumbing situations.

A trap blocks sewer gases in drainage lines, not backflow into the water supply. Venting helps balance pressure in the drainage system but does not stop backflow into the potable supply. A backflow preventer can stop backflow, but it’s a device installed where risk is identified and isn’t universally required for every fixture.