When installing water supply lines, what is a common requirement for backflow prevention?

Backflow prevention is crucial in plumbing systems to ensure that contaminated water does not flow back into the potable water supply. An air gap is the most effective method for preventing backflow and is often mandated by plumbing codes.

An air gap is a physical separation between the end of a water supply line and the flood level of a fixture. This gap prevents backflow by ensuring that even if pressure in the plumbing system drops, contaminated water cannot siphon back into the clean water supply. It is often used in applications such as sinks, where a direct connection to the sewer system may pose a risk of contamination.

While other types of check valves can help in certain situations, they may not be sufficient alone to ensure complete backflow protection as they rely on mechanical closure or pressure differences to function. An air gap, however, completely eliminates the possibility of reverse flow because it physically separates the two systems. Thus, in many situations, especially those involving critical connections, the air gap is the preferred requirement for backflow prevention in water supply lines.