What does "water hammer" refer to in plumbing?

"Water hammer" refers to a phenomenon in plumbing characterized by a knocking or banging sound in pipes, which occurs when the flow of water is suddenly stopped or changed direction. This abrupt change creates a shock wave that travels through the water in the pipes, causing pressure fluctuations and resulting in the audible knocking noise. It typically happens when a valve is closed quickly, leading to a sudden halt in water movement. This condition can potentially lead to issues like pipe damage or leaks if not addressed, making it an important concept in plumbing systems.

The other choices represent different plumbing concepts: backflow prevention valves are designed to stop reverse flow of water, pipe joints refer to the connections between sections of piping, and methods for testing pipe integrity involve checking for leaks or weaknesses in the piping system. These do not relate to the specific phenomenon of water hammer.