What Causes Pipes to Have a Knocking Sound When Water Is Turned On?

Updated February 21, 2017

Knocking pipes can wake you up in the middle of the night or make showering into a noisy experience. These pipes can also be damaged by the movement causing the knocking noises. There are a few different causes of noisy pipes, some of which can be repaired by the homeowner.

Water Hammer

Water hammer, also known as air hammer, is a loud knocking sound that is caused by the pressurisation of a water pipe when the water is shut off, according to Inspectapedia. Knocking noises from water hammer only occur when a faucet or water connection is closed. However, if an appliance or faucet switches on and off rapidly, the knocks may sound like they are being caused by the water being turned on. A simple water hammer suppression device can be installed on the appliance or faucet causing the noise.

Loose Valves

Loose or broken valves of all kinds can cause knocking, rattling or other noises in water pipes when water flow is switched on. The Home and Garden Site says that a loose valve at the faucet in a shower can knock or rattle loudly at any time of day, but especially when the water in the shower is turned on. Faucet valve stems and fill valves in toilets will also make knocking noises if they are loose or broken when the faucet is turned on or the toilet is flushed, according to

Loose Support Straps

Water hammer, rust and other problems can lead to broken or loose support straps around water pipes. Once these straps are loose, even normal water pressure will make them rock back and forth, according to The Natural Handyman. Rocking water pipes will hit floor joists and wall supports, knocking on them loudly. This constant movement loosens the connections between pipes, especially at joints, and may lead to leaks. Tightening or replacing broken support straps usually fixes this problem.

High Water Pressure

The experts at say that a home should have, at maximum, 60 PSI of water pressure in its pipes. Water pressure above this level causes pipes to move more than usual as water travels through them. This leads to loosened support straps and can put pressure on joints and connectors and cause serious leaks. Hammering or knocking noises when a faucet or valve is opened is often caused by high water pressure, with the sound occurring as the pressure inside the pipe builds.

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About the Author

Jessica Kolifrath is a competent copywriter who has been writing professionally since 2008. She is based in the Atlanta area but travels around the Southeastern United States regularly. She currently holds an associate degree in psychology and is pursuing a bachelor's degree in the field.