Water hammer is a phenomenon that occurs in plumbing systems when a fluid in motion is suddenly forced to stop or change direction. This abrupt change creates a pressure surge, resulting in a loud banging noise in pipes. It often happens when valves are closed quickly, causing the water to slam against the closed valve. The effects of water hammer can lead to damage in pipes and fixtures over time. To prevent this issue, devices like water hammer arrestors can be installed. These devices absorb the shock wave created by the sudden stop of water flow, helping to maintain a stable pressure in the plumbing system.