What is one effective way to prevent backflow?

• A. Using an appropriately placed air gap
• B. A larger pipe
• C. Increasing water heater temperature
• D. Moving the source of water upstream

Answer: (A)

Preventing backflow relies on creating a physical separation between the clean water supply and any potential source of contamination. An air gap does this by leaving a gap, typically vertical, between the end of the potable-water outlet and the top edge of the sink or drain. That gap ensures that even if pressure in the system drops or changes, contaminated water cannot be drawn back into the clean supply because there is no direct contact or connection for reverse flow. It’s a simple, passive barrier that doesn’t rely on valves or pressure conditions to function.

In contrast, a larger pipe doesn’t stop backflow; it may change flow dynamics but doesn’t break the potential path for reverse flow. Increasing water heater temperature doesn’t address the problem and can create safety risks like scalding. Moving the water source upstream doesn’t inherently prevent backflow either and could introduce other complications without a true backflow-prevention method. The air gap provides a reliable, straightforward way to keep the potable supply isolated from non-potable sources.