Why do my pipes bang when I turn off the water?

Banging pipes when a faucet or appliance shuts off can be water hammer, a pressure surge caused by a sudden stop in water flow. Loose pipe supports and high water pressure may make the noise worse, although sound alone does not establish the cause. Note which fixture triggers it and whether the sound is new or getting louder. Do not try to fix the problem by simply shutting the home's main valve halfway. A plumber can measure pressure, inspect loose connections and decide whether an appropriate water-hammer arrestor, pressure adjustment or another repair is needed.