What is Water Hammer and How to Fix It?

What is Water Hammer?

Water hammer, technically referred to as hydraulic shock, occurs when a moving column of water is suddenly forced to stop or change direction. The sudden stop creates a shockwave that sends vibrations through the pipes, resulting in a loud banging noise. These shockwaves are especially forceful in homes with high water pressure or older plumbing systems.

What Causes Water Hammer?

There are several common causes of water hammer in residential plumbing systems:

Fast-Closing Valves: Appliances like washing machines and dishwashers use solenoid valves that close very quickly. When the water flow is shut off instantly, it creates a sudden pressure surge, resulting in water hammer.

High Water Pressure: When the water pressure in your home is too high, it increases the force behind the water flow, making any sudden stops much more violent.

Lack of Air Chambers: Most plumbing systems have vertical air chambers or water hammer arrestors near valves to absorb pressure. Over time, these chambers can fill with water and eliminate the cushion they’re designed to provide.

Loose Pipes: If your plumbing pipes are not properly secured, they can move or rattle against the wall studs or joists when the pressure wave travels through them.

How to Fix Water Hammer

Fortunately, water hammer can be corrected with a few straightforward solutions—some DIY and others best left to a professional plumbing repair service.

Install or Recharge Air Chambers

Air chambers are vertical pipes installed near valves that act as shock absorbers. If they’ve filled with water, they need to be drained and refilled with air. This can sometimes be done by turning off your main water supply and draining the pipes completely.

Install Water Hammer Arrestors

If your home doesn’t have air chambers or if they’re ineffective, a plumber can install water hammer arrestors, which are specially designed to absorb the shock and prevent the banging noise.

Lower Your Water Pressure

Installing a pressure-reducing valve (PRV) can help bring your home's water pressure down to a safe and manageable level. Normal residential water pressure should be between 40–60 psi. If your water pressure seems to be fluctuating, call a nearby plumbing repair service to find the source of the problem and make repairs.