What Causes Water Pipes to Whistle?

It's usually bothersome, but sometimes whistling from water pipes verges on the melodious and soothing. If the latter, it's OK to relax a little, but if the sounds are alarming, then be alarmed. Whistling sounds are often caused by high water pressure, and just as they do when people and animals make them, they often get louder and more intense when something is about to happen.

The Sound of Turbulence

Whether you hear the whistling from a faucet, a toilet fill valve or from somewhere inside the wall, it's telling you that water is flowing. When you hear the sounds from a faucet or valve, it's usually produced by a worn gasket or washer flapping harmonically in tune with the eddy currents of he emerging water. When you hear it from the pipes, though, it's a sign that the water turbulence is higher than it should be. Possible reasons are:

• The water pressure is too high. 
  
• The pipes are old, and mineral deposits inside are restricting water flow.
  
• Water is flowing erratically through a poorly placed fitting, such as an elbow or tee.
  
• Air has gotten into the pipes, forming a bubble that restricts water flow.
  
• An inline valve is partially open when it should be open all the way.
  

The Pressure's On

Check the Pressure

A simple test can confirm that the water pressure is higher than it should be. Screw a pressure gauge onto a threaded faucet -- usually an outdoor one or one in the laundry room -- turn the faucet on all the way and watch the needle. The pressure shouldn't be much higher than 60 pounds per square inch. If you have a well, keep the gauge connected until the pump cycles on and finishes pressurizing the system.

Reduce the Pressure

Adjust the pressure regulator. If your home is connected to a municipal water supply, you should have a pressure regulator installed near the water meter. Reduce the pressure by turning the nut on the top of the regulator clockwise, using a wrench.

Adjust the pump cut-off pressure. If you get your water from a well, you adjust the pressure by setting the pump cut-off pressure lower than its current setting. This is an adjustment you make to the pressure switch; since this adjustment involves exposing 240-volt electrical terminals, you should get a plumber to do it for you.

All of these problems can have undesirable consequences. For example, mineral deposits can break loose and cause clogs, air bubbles can actually stop water from flowing, and poorly placed fittings usually vibrate as well as whistle, which weakens the joints and causes leaks. High water pressure is the most serious problem, though. It can lead to joint failures and leaks in multiple places, some behind walls where water can do extensive damage before you know it's there.

Purge the Air

When air gets into water pipes, it rises to the highest point and may remain in a horizontal section to form a bubble. The highest parts of the pipes are usually in the upstairs bathrooms or the walls near those bathrooms. To purge the air, turn on all the faucets in the bathroom at the same time while you flush the toilets. The increased flow of water should dislodge the bubble and push it out through a faucet.

Change the Pipes

If the whistling sounds come from old galvanized steel piping, they are almost certainly the result of corrosion inside the pipes. Unfortunately, there's no easy fix -- you need to replace the affected pipes. You can take consolation in the fact that, by replacing the pipes, your plumbing will work better and you'll be averting other problems, such as leaks, that were bound to happen next.

Similarly, if you've pinpointed the whistling sound to a particular fitting, the solution is to reroute the pipes to avoid the need for that fitting. That's also a retrofit that will probably improve the water flow in your pipes.