Quieting water hammer

House Doctor | Gary Dymski

September 15, 2005

My water pipes make a tremendous amount of noise when I turn on my dishwasher. I am afraid they will break loose. If I turn on the hot water at the sink, the noise stops. Any suggestions? -- J. Sele, Rocky Point

You have something commonly called "water hammer," which is a pressure shock wave induced in plumbing-supply systems whenever there is a sudden change in the flow of water. For example, when the dishwasher is turned on and calls for hot water, kinetic energy is created in a direction opposite the water flow. This energy creates the water hammer, which can damage pipes and valves and eventually weaken joints. Some causes of water hammer include improperly sized supply lines, high water pressure, inadequate strapping of plumbing lines to wood joists or studs, excessively long straight supply line runs without turns and the lack of an expansion tank.

A plumber might need to examine the installation of the dishwasher to determine if water pressure is excessive or if an expansion tank has been installed on your supply line. You also might try strapping the supply lines inside your cabinets or in your basement.

The plumber could install a device called a water-hammer arrester on the hot-water line running to the dishwasher. These arresters often are made for specific appliances - one size for the dishwasher, for example, and another for the washing machine - and run $10 to $15 apiece. They're available at home centers and plumbing supply stores.