Water hammer
The bang in your pipes when fast-moving water is stopped suddenly.
Water hammer is the loud thud or banging you hear when a valve closes quickly — a washing-machine or dishwasher solenoid, or a faucet shut off fast. The moving column of water slams to a stop and sends a pressure shock wave back through the pipes, which can loosen joints and, over time, cause leaks. Common fixes are air chambers or mechanical water-hammer arrestors at the offending fixture, securing loose pipes, and confirming your home's water pressure isn't too high. A missing or waterlogged [expansion tank](/glossary/expansion-tank) can make it worse. See [banging pipes (water hammer)](/guides/water-hammer-banging-pipes) for the full fix.