Everything is relative. You know how the drip, drip, drip from the leaky faucet in the bathroom sink will seem as loud as a bass drum, keeping you up all night? In the daytime you never heard or noticed it. But now, in the middle of the night, when the house is quiet and free of distracting noises, it’s loud and clear.

That’s why, in years gone by, professionals used to locate leaky pipes by using the quiet time in the middle of the night to isolate the sound of escaping water. While this technique can be effective in a residential setting, it has limitations in facilities that run 24/7. Fortunately, professionals now have a second option: Magnifying the sound of the leak so that it’s much louder than the background noise. Again, everything is relative.

Water leak locators use specially designed sensors that listen for the gurgling or hammering of a cracked pipe below ground. A ground sensor locates through hard surfaces like concrete, asphalt, and tile. A probe sensor picks up leaks through soft surfaces such as grass or carpet, or it can be used as a contact probe on above ground pipes or hydrants. Both should have shock-resistant housings to reduce unwanted noise.

Safety tip: In order to preserve your hearing, always use a leak locator with a safety switch to protect you from sudden loud noises by muting the sound when the button is released.

Before getting started, it’s helpful to know what a leak sounds like. Leak sounds are created by three different situations:

1. Pipe vibration, the loudest and easiest to detect, is caused by water forced through a crack in the pipe and makes a whooshing or hissing sound.

2. Water forced through the crack hits the surrounding soil. The type of material around the pipe affects this sound. If it’s rock or gravel, hammering or knocking sounds may be heard. If loose soil surrounds the pipe, it may be difficult to hear anything at all.

3. Water flowing through the soil cavity will create a gurgling sound like a small stream or brook.

Loose or sandy soil, swampy or water-saturated areas, and newly buried pipe produce muffled leak sounds that can be harder to find. Thus, a pipe that’s been leaking for some time will absorb the leak vibrations, making it more difficult to find. Pipe in rocky or hard ground transmits leak sounds best.

If you are new to leak location, you must learn the sound of a leak before you start your search.

If you are new to leak location, you must learn the sound of a leak before you start your search. Set up the water leak locator with the probe sensor attachment. Touch the tip of the probe bar to the cold water line under a sink. Then, turn on the valve just a little bit so the water is dribbling out of the faucet. This simulates the sound of a leak. Turn the valve on and off as you listen until you hear the difference.

The loudness and frequency of the leak noise is affected by the water pressure, pipe material, soil density and type, depth of the pipe, and type of surface (concrete, grass, etc.). The higher the pressure, the louder the leak sounds will be.

Which gets us back to the trick that we hinted about earlier: In order to amplify the sound of the leak so that it seems to jump out from the background noise, one trick is to inject air into the leaking water line at a slightly higher psi than the water pressure. When the combination of air and water escape from the pipe through the leak at high pressure, the sound is many times louder than water leak alone. All you need is an air compressor and a device similar to General’s Sound Amplification Manifold (SAM). Be careful not to add more than 10-15 psi of air pressure above the incoming water pressure or you could damage the seals in the fixtures within the house.

The most common indicators of a domestic water leak are a dramatic increase in a water bill or hearing water running all the time.

If you don’t see any obvious evidence of a major water leak, like “ponding” or loud leak sounds, then start a water leak survey. Use the locator’s probe sensor to survey the hydrants and main valves. If you hear the sound of a leak at one location, check lines running in all directions from that point. The leak location is usually found between the loudest and second loudest survey locations. Suspect older parts of the system or areas with a history of leaks, and of course, any recent excavations. Then you can begin to narrow down your search.

Start by locating the route of the water line by using a digital pipe locator and transmitter. Attach the transmitter leads to each end of the pipe to be located, and then turn on the transmitter. Most modern systems (like the General Hot Spot Transmitter) will let you know when you have achieved a good connection and even indicate the signal strength. Follow the directions and clearly mark the surface as you locate the path of the water line.

Select the appropriate sensor. Then, walk the line, taking a reading every 3 or 4 feet. Follow the flow of the water line, from upstream to downstream, and note each reading. Do not adjust the volume control. The volume must remain constant in order to make accurate comparisons.

While this process is more of an art than a science, it doesn’t take long to gain a respectable level of proficiency. With patience and practice, you’ll be locating even small leaks before you know it. Happy Hunting!