An open, physical separation between a potable water supply line and a non-potable appliance or fixture prevents contaminated water from being siphoned back into the drinking water system due to backflow. This separation, often achieved through a vertical air space, is critical for appliances like clothes washers and dishwashers, protecting against potential health hazards. A dedicated faucet with an attached hose, elevated above the flood rim of the sink or appliance standpipe, serves as a common illustration of this principle.
This protective measure is mandated by plumbing codes in many regions to safeguard public health. Preventing backflow of contaminated water into the clean water supply is paramount, and this method offers a simple, yet effective solution. Its historical development stems from growing awareness of potential cross-contamination risks and the need for robust preventative measures in residential plumbing systems. The resulting plumbing codes and practices offer crucial safeguards against waterborne illnesses.