What does backflow refer to?

Backflow refers to the flow of liquids, gases, or other substances in the opposite direction from where they are intended to go within a plumbing system. This term is particularly important in the context of water supply systems, where backflow can lead to contamination of potable water with non-potable substances.

In a plumbing system, there are mechanisms such as backflow preventers designed to combat this issue, ensuring that water flows correctly from the supply source to fixtures and appliances. Understanding backflow is crucial for maintaining health and safety standards in any facility that serves food or beverages, as improper flow can compromise the safety of the water supply and potentially lead to serious health risks.

The other choices do not accurately describe backflow: the flow of gas in plumbing systems does not address the context of liquids being drawn back into a water supply; flow in the intended direction is essentially the opposite of backflow; and flow stopping in a water line pertains to a complete halt rather than the reverse movement of the fluid.