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What causes water hammer and is it damaging?

The short answer

Water hammer is the shock wave created when fast-moving water is stopped suddenly by a quick-closing valve. It is fixable, and left alone it can loosen fittings and eventually cause leaks.

TradieAnswers editorial · written in-house and sourced to the authorities listed below

Checked against 4 published sources, listed in full at the end of this page. How we source this

Water in a pipe has momentum. When a valve slams shut, that momentum has nowhere to go and converts into a pressure spike that travels back along the pipe as a bang. Loose or unsupported pipework then amplifies it into the noise you hear through the wall.

Common triggers

  • Washing machine and dishwasher solenoid valves, which close in milliseconds by design.
  • Quarter-turn taps and mixers, which close far faster than the old washer taps the house was plumbed for.
  • Mains pressure that is too high, which makes every event worse.
  • Pipework that was never clipped properly in the wall or under the floor.

What actually fixes it

A water hammer arrestor near the offending appliance absorbs the spike. Correctly clipping pipework stops it becoming audible. If pressure at the meter is high, fitting or adjusting a pressure limiting valve addresses the cause rather than the symptom, and it also extends the life of every flexible hose, mixer and appliance in the house.

Sources

Every source below was fetched and its response recorded on the date shown. Where a government site blocks automated clients, that is noted rather than reported as a successful check.

  1. NCC 2022 Volume Three: Plumbing Code of Australia · Australian Building Codes BoardChecked 2026-08-11 · responded 200 OK
  2. Backflow prevention · Sydney WaterChecked 2026-08-10 · responded 200 OK
  3. Building and Plumbing Commission · Building and Plumbing Commission VictoriaChecked 2026-08-10 · live, but blocks automated clients so the specific page could not be confirmed
  4. Water Rating (WELS) · Australian GovernmentChecked 2026-08-10 · responded 200 OK

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