Master the IRC Plumbing Puzzle 2025 – Dive into Code Success!

To protect the water supply to a dishwasher against backflow, an air gap is required. An air gap creates a physical separation between the water supply line and the discharge line of the dishwasher, which prevents contaminated water from siphoning back into the potable water supply. This is a critical safeguard to ensure that the drinking water remains clean and safe. The air gap must be installed at a specified height above the flood level of the sink or receptacle where the dishwasher drains, according to the International Residential Code.

Other forms of backflow protection, such as check valves, do exist but are not as effective in preventing backflow in this particular application as an air gap. While check valves can prevent reverse flow due to pressure changes, they do not provide the physical separation needed to ensure that contaminated water cannot make its way back into the clean water supply. A backwater valve is intended for use in drainage systems to prevent backflow during flooding but does not serve the same purpose as an air gap in this context. A pressure relief valve primarily protects against excessive pressure in water supply systems and is not designed for backflow prevention in dishwashers.