Water Hammer: What Is It and How Do You Fix It?

A loud banging or thudding noise from your pipes when you turn a tap on or off — that’s water hammer. It’s one of the most common and most misunderstood plumbing problems in Melbourne homes. Here’s what it is, what causes it, whether it’s serious, and how to fix it.

What Is Water Hammer?

Water hammer (technically called hydraulic shock) occurs when fast-flowing water in a pipe is suddenly stopped or redirected. The kinetic energy in the moving water has to go somewhere — and it does, as a pressure wave that slams into the pipe walls and fittings. The result is that characteristic bang or thump you hear when you quickly shut off a tap, or when a washing machine solenoid valve closes.

What Causes Water Hammer?

• High water pressure — The most common cause. Melbourne’s mains water pressure can be high, and anything above 500kPa significantly increases water hammer risk
• Long straight pipe runs — Water builds up more momentum in long straight sections
• Quick-closing valves — Modern washing machines, dishwashers, and solenoid valves close almost instantly, causing sudden pressure shocks
• Loose pipe brackets — Pipes that aren’t properly secured to walls or joists rattle and bang more when hammer occurs
• No air chambers or hammer arrestors — Older homes didn’t have these; newer plumbing codes require them

Is Water Hammer Serious?

Occasional mild water hammer is generally not an immediate emergency. But if it’s happening frequently or severely, it can:

• Damage pipe joints and fittings over time
• Cause micro-fractures that lead to leaks
• Damage appliance connections and solenoid valves
• Loosen pipe brackets, leading to rattling and vibration damage

Severe or frequent water hammer should be addressed rather than ignored.

How to Fix Water Hammer

• Install a pressure limiting valve (PLV) — This is the most effective fix if high pressure is the cause. A PLV reduces mains pressure to a safe level (typically 350–500kPa) for the entire property. A licensed plumber must install this.
• Install water hammer arrestors — Small devices installed at the offending valve (like a washing machine tap) that absorb the pressure shock.
• Re-secure loose pipe brackets — Tightening or adding pipe clips stops rattling and reduces the transmission of noise.
• Re-fill air chambers — Older homes used air-filled chambers in the pipe system to cushion hammer. These can waterlog over time and stop working. Draining the system briefly can re-introduce air.