Fixing Faucet Water Hammer Noise

What Is Water Hammer?

Water hammer is the loud banging or thudding sound that occurs when water flow is suddenly stopped, such as when a faucet is quickly turned off or a washing machine valve closes. The noise is caused by the momentum of moving water slamming against the closed valve, creating a pressure shockwave that travels through your pipes. Besides being annoying, water hammer can damage pipe joints, valves, and appliance connections over time.

Recharging Air Chambers

Many homes have air chambers — short vertical pipes installed near fixtures that act as cushions to absorb the pressure shock. Over time, these chambers can fill with water and lose their effectiveness. To recharge them, turn off the main water supply, open the highest and lowest faucets in your home to drain all water from the pipes, then close the faucets and turn the water back on. This refills the air chambers with air. If this solves the problem temporarily but it returns, the air chambers may need to be replaced with mechanical water hammer arrestors.

Installing Water Hammer Arrestors

Water hammer arrestors are sealed devices containing a piston or diaphragm and a compressed air chamber. They connect directly to the water supply line near the offending fixture. For faucets, install them on the hot and cold supply lines under the sink using a tee fitting. For washing machines, screw-on arrestors connect directly to the washing machine valve outlets. Choose arrestors rated for your water pressure and pipe size — most residential applications use 3/8-inch or 1/2-inch models.

Other Solutions

If water hammer occurs throughout your home, your water pressure may be too high. Check it with a pressure gauge on an outdoor hose bib — residential pressure should be between 40 and 80 psi. If it exceeds 80 psi, install or adjust a pressure-reducing valve on your main water line. Loose pipes can amplify water hammer noise, so secure any pipes that rattle or vibrate using pipe straps or cushioned hangers. Quick-closing quarter-turn faucets and lever-style handles are more prone to water hammer than slow-closing multi-turn handles.