In plumbing, what does the term "backflow" refer to?

The term "backflow" in plumbing specifically refers to the flow of water in the opposite direction from its intended path. This occurs when the normal pressure of the water system is disrupted, often due to a drop in pressure, creating a situation where contaminated water can flow back into the clean water supply. This is a critical concern for public health and safety, as it can lead to the contamination of drinking water sources.

Preventative measures such as backflow preventers, which are installed in plumbing systems, ensure that water does not flow back into the supply line. Understanding backflow is vital for inspectors to ensure compliance with plumbing codes and to protect the integrity of the water system.

The other choices describe different plumbing phenomena but do not accurately capture the definition of backflow. The accumulation of water in a trap pertains to the function of traps in preventing sewer gases from entering the home, pressure build-up in pipes relates more to issues with pipe integrity or water hammer, and overflow from a fixture deals with the excess water spilling over when a fixture is filled beyond its capacity. Each of these situations impacts plumbing systems but does not define the concept of backflow.