What causes water hammer?

What causes water hammer?

Ever heard a banging or clanging when you turn off your taps? This blog looks at the causes and solutions of water hammer.
‘Water hammer’ can be identified as pipes that bang, clang and vibrate when you turn off your taps. As well as being extremely noisy, water hammer can cause water heaters, joints, seals and connections to fail, and taps to leak.

What causes it?

Water hammer is a shock wave of high water pressure in the pipes, caused by the sudden closing of a valve. The water does not compress, but crashes into the closed valve again and again, creating a loud hammering noise. The valve eventually disintegrates within the piping system. There are several common causes of water hammer, including:

  • Poor pipe installation
  • ‘Flick mixer’ taps (Typical example shown opposite)
  • Faulty tap washers
  • Solenoid valves on appliances such as dishwashers and washing machines
  • High water pressure


What are the solutions?

  • Instead of ‘flick mixer’ taps that shut the water off suddenly, choose ‘soft close’ mixer taps with a built-in shock absorber system.
  • If vibrating pipes occur in a particular area, for example the kitchen, it may help to replace plastic or ceramic tap washers with brass tap washers. Ceramic washers can break easily, and when that happens you may have to shut off the water at the mains and call a plumber to repair the tap.
  • Install taps with washers that can be easily replaced, minimising the cost of replacement should the need arise.
  • Install water hammer arresters on washing machine taps. Often the solenoid valve in washing machines causes the pipes to rattle and clunk.
  • Reducing your water pressure can reduce water hammer. Call a plumber and have a ‘pressure limiting valve’ or water hammer arrester installed.
  • Check with local water authorities for regulations.

We must note that all plumbing works must be undertaken by a licensed plumber. In Western Australia it is illegal for non-certified plumbers to perform any kind of plumbing works.

Author: Lewis Flatt – Cap-It-All Building Inspections, Servicing the Perth Metro Area

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