Thumping Noise When I Turn the Faucet On

If you hear a thumping noise when you turn on your faucet, you probably also hear thumps when you turn it off. The thumping is caused by _water hammer_, and it isn't good for the pipes or the faucet. In fact, water hammer has been known to break faucets in half. That probably won't happen to your faucet, but if left unmanaged, water hammer might eventually weaken the pipe joints and cause a leak.

What Is Water Hammer?

Water is an incompressible fluid, and it generates turbulence when it flows inside a pressurized pipe. The turbulence is unnoticeable when all valves are completely open and the flow is steady, but when the flow changes as you open or close a valve, it can send shock waves through the fluid, which transfers the shocks to the walls of the pipe. These shocks are what is known as water hammer -- and the likelihood of actual noises depends on the water pressure, the characteristics of the valve opening and its orientation with respect to the general flow -- a 90-degree bend in the pipes just before the faucet opening makes thumping more likely.

What to Do

Reducing the water pressure may eliminate water hammer.

  • Turn down the pressure regulator for the house water supply -- this is an especially good strategy if you hear thumping at more than one fixture.
  • Reduce the cut-off pressure of the pressure pump, if your house is serviced by a well.
  • Adjust the pressure to the faucet by partially closing the shut-off valves under the sink.

Reducing the water pressure may not work. If it doesn't, you need to make some modification to the pipes. Replacing the hammering pipes with larger ones works, but it's seldom practical. Instead, install a water hammer arrestor, also known as a surge arrestor.

Installing a Surge Arrestor

A surge arrestor is a small length of copper pipe that's closed at one end to form a bulb. Inside is a sliding piston that absorbs the pressure created by water turbulence -- the piston compresses air in the chamber created by itself and the closed end of the bulb. Install surge arrestors in one of two ways:

  • Solder them into the hot and cold water lines as close to the shut-off valves as possible. Soldering a surge arrestor is no more complicated than soldering a coupling, although you may have to move a cabinet or break into a wall to do it.
  • Screw one to each of the shut-off valves. Some surge arrestors come with male and female thread connectors that allow you to install them between the supply hoses and the valves. This is the easier option, provided you have room for the arrestors under the sink.