How to Install a Water Hammer Arrester

Steps for Putting an Arrester on a Washing Machine

Washing machine turned on with water supply hoses connected to water hammer arresters

The Spruce / Kevin Norris

Project Overview
  • Working Time: 30 mins - 1 hr
  • Total Time: 30 mins - 1 hr
  • Skill Level: Beginner
  • Estimated Cost: $25

If you hear banging, rattling and other odd sounds coming from inside your walls or floors, and the noises seem to coincide with flushing the toilet or running the washing machine, chances are you've got water hammer. Water hammer occurs in water supply piping and is caused by the sudden stop or change in direction of water flow, such as when a washing machine or toilet stops filling from a quick closing valve. Usually, water hammer does not cause any damage to plumbing, but in extreme cases it can lead to failure in fittings or pipes.

Water hammer arresters are simple devices that install within the water line to a specific fixture or appliance. Arresters absorb the shock wave created by a sudden stoppage of the water flow. Installing a water arrester on each line supplying the offending fixture (or fixtures) usually solves the problem. However, if the problem seems to be widespread, you may want to start by testing your home's water pressure to make sure it's not too high.

Checking Your Water Pressure

Often you will hear much more hammering and knocking noises when the household water pressure is too high. Test the water pressure with a gauge that can screw onto an exterior hose bib or behind the washing machine. If the pressure is above 75 pounds per square inch (psi), you may need to have a pressure regulator installed or, if you have a regulator, it may have gone bad and should be replaced.

What You'll Need

Equipment / Tools

  • Tongue-and-groove pliers


  • Water hammer arresters


Materials and tools to install a water hammer arrester

The Spruce / Kevin Norris

  1. Identify the Cause

    Observe carefully to determine what appliance or fixture seems to be causing the banging in your pipes. The most common culprits include washing machines, dishwashers, toilets, and refrigerator ice makers or water dispensers. All of these appliances have solenoid valves that shut off the water instantly, unlike a faucet, which reduces the water flow until it is shut off completely.

    Washing machine water supply hoses being inspected

    The Spruce / Kevin Norris

  2. Determine an Action Plan

    If the washing machine water supply is the culprit, then install water hammer arresters on both the hot and cold water supply lines. The easiest type to install are simple screw-on devices that fit onto the faucet spigots where the washing machine hoses are connected. There are similar devices for other types of appliances and water supplies.

    Water hammer arrester held in front of washing machine water supply hoses

    The Spruce / Kevin Norris

  3. Turn Off the Water and Disconnect the Hoses

    Shut off the valves on the washing machine hoses tightly, then disconnect the hoses from the valves. Take care that you do not lose the washers at the end of the hoses.

    Water supply hoses disconnected from shut off valves

    The Spruce / Kevin Norris

  4. Connect the Water Hammer Arresters

    Thread a water hammer arrester onto each water supply valve, making it hand-tight. Then, snug it up a bit more with tongue-and-groove pliers, but be careful not to overtighten.


    Most water hammer arresters are installed on the washing machine valves, but the instructions may recommend connecting them directly to the back of the washing machine in order to protect the washer hoses. The issue with installing them here is that it can make the washing machine sit farther away from the wall. If space is too tight, then connecting the arresters to the valves may be the only option.

    Water hammer arresters threaded to water supply valves

    The Spruce / Kevin Norris

  5. Connect the Washer Hoses

    Connect the washer hoses onto the water hammer arresters, taking care to make sure that you match up the hot water hose to the hot water supply. Tighten each connection carefully with the pliers.

    Water supply tubes connected to water hammer arresters

    The Spruce / Kevin Norris

  6. Turn on the Water

    Turn the water back on and check for leaks. If any joints are leaking, tighten them just a bit more, using the pliers. The arresters will work at any angle, so position them however they best they work for your situation.

    Water supply valve handles turned on to check leaks

    The Spruce / Kevin Norris

Toilet Installation

If you find that your water hammer is originating when you flush a particular toilet, you'll want to install your arrester on the water fill line, To install one there, first turn off the water by turning the football-shaped knob all the way in the clockwise direction. Then, unscrew the line from the toilet tank, screw the water hammer arrester onto the threads at the bottom of the tank, and attach the water line to the other side of the arrester. Plumber's tape on the threads will help secure the installation.

When everything looks good, turn the water back on, check for leaks, and give the toilet a flush to make sure the hammering is eliminated.

Other Installations

Sometimes, you might find that the best place to install a water hammer arrester is somewhere that doesn't provide easy access to shut-off valves or threaded connectors. In this case, you will need to purchase and install a T-shaped fitting into which your water hammer arrester can be attached. You'll need to cut into the pipe, install the fitting, and connect the arrester to the threaded outlet on the side of the fitting. Again, using plumber's tape before screwing in the arrester will help prevent leakage.