Water Hammer / Noisy Pipes: Cause, Effect, Solution

March 15, 2008 | by Ethan (email) |

Water hammer is a tapping or hammering sound in water pipes caused by the pipes knocking into one another or other nearby obstacles (e.g. brick, block, wood, sinks, toilets, fixtures, etc). Copper pipes are most commonly affected/noticed; however, the root causes of water hammer can exist in any pressurized pipe system.

What Causes Water Hammer?

Water hammer is caused by pressure that has rapidly built up in the water line and is looking for a place to go. It usually originates from a valve where the flow of water is quickly turned off. Older pipes can come unanchored, causing even small pressure spikes to create water hammer noises. Less common sources include well water pumps and defective water hammer protection devices.

Effects of Water Hammer

water hammer, water knocking primarily affects copper pipesWater Hammer is more dangerous than you may realize. The pressure that originates at your valve is transfered to the entire volume of water in the pipe. These surges travel faster than the speed of sound and exert huge amounts of pressure at any given point. Over time, pipes and joints will weaken and begin leaking.

How to Solve/Stop Water Hammer

Ever wonder what that PVC pipe is on your roof? It’s connected to your water sewer pipes. As water flows out of your house, this open connection releases pressure and allows your water to flow freely. (That’s why you don’t have a water hammer problem on the non-pressurized side of the system). A similar concept applies to solving water hammer problems on the pressurized side: create an outlet for the excessive pressure (or eliminate the higher pressure in the first place).

1. Swap out the valve that is closing too quickly. You can install automatically closing valves that close slowly. These are controlled by the flow of water and do not need electricity to operate. If the water hammer is being caused by a built-in fixture, like a toilet, dishwasher, washing machine, or faucet, you will likely need to replace the valve component in that fixture, or use an alternative method described below.

2. Install an air chamber. These chambers are simply pockets of air. The surge compresses the air and absorbs all the pressure. These chambers are usually seen behind a sink or other appliance where water hammer occurs frequently. They look like upside-down bottles attached to the pipe.

3. Install air valves. These simply allow air in to relieve the pressure. Air valves are effective but at the cost of having unwanted air in your water supply. Also these valves can create noises of their own. Be sure to select the right size valve for your pipe. Typical water main pipe is 3/4 inch. For these, install a 1/2 inch release valve.

What do you think? Water pipes can make lots of noises. What problems have you come across? How’d you solve them?

8 Responses
  1. Jon says:

    Must be something for houses north of the Mason Dixon line. I’ve lived in a couple of house and apartments through “The South” and never had any hammer issues….


  2. Bill Hutchison says:

    I actually found that just shutting off the water going into our washing machine when the machine isn’t in use cut down on our water hammer.

    Other then that I was told to add an inline adapter to our washing machine to cut out on the hammer.

  3. Ethan says:


    Not sure if your just lucky or if there really is something about about your location.


    Did you just keep turning the water off or did you install the inline? Does the inline create any noises of its own?

  4. steve says:

    Another solution is Anti-Hammer tap valves. These did the job for me. The ones I used are manufactured in Australia. Here’s my post:


  5. I’ll respond to Ethan here as well…

    I didn’t bother getting the inline. I just turn the water on and off when I do the laundry and that has solved my hammer problem.

    I’m probably just cheap though, as I was told the inline adapters are actually quite cheap.

  6. tom says:

    wow… I’m a new reader and I was browsing through your site and found this post… I’ve always wondered what was that racket every time the washing machine stops pulling in water. Now I know. I found these online and will be installing them today…


  7. SpinMan says:

    My particular problem isn’t quite air hammer. It just sounds like it. Turns out that the hot and cold water pipes in the basement are supported by hangers, but there is a right angle that is not supported. Every time a valve opens, the corner bangs into the header for a basement wall. I’ve tried installing more pipe clamps, but that hasn’t helped at all. Any suggestions?

  8. Joh Young says:

    I I slowly turn on the hot water tap in the washroom, everything is OK, but when it’s turn on full (or even less) there’s a helluva racket. Sounds like water hammer, but maybe not. The cold water tap is fine, just the hot water.

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