How To Test For A Water Line Leak Or Water Main Break: A Helpful Guide

Accurately determining if you have a water line leak requires no special tools or equipment. But it does require care and patience using a step-by-step process. If you are a homeowner, you can perform the test yourself using this guide. But in most cases calling both a licensed plumber and your local water authority is usually the best bet. Typically you will incur little or no cost for verifying a leak. A water line leak can add substantially to your water bill, so prompt action is advisable. Understanding how to determine if you have a leak, and perform a leak test, is therefore good to know. What follows is a commonsense and easy to follow 3 step guide on how to check for various types of water leaks.

water valves on a line

Always close the valve closest to inside of building on the main line

Locate Your Main Line To Check For Water Line Leaks

Virtually all houses in NYC now have a water meter. The meter is connected just on the house side of the main control valve for the service line from the street. The  water service line will be the largest fresh water pipe inside your house. It can also be easy to pinpoint because it will have a ground clamp. The ground clamp is for a secondary ground for the electrical supply for your house. There should not be any electricity flowing through the electric ground wire attached to your water service line. The ground on your water line is designed to act as a backup for the main electrical ground.

meter dials

Typical old style mechanical water meter

Each water meter is designed a little bit differently. The top of older mechanical water meters typically have a dial. There are various indicators that move or spin when water is being used. The smallest of these dials is referred to as a ‘leak dial’. If no water is being used in the house this dial and none of the other dials should be moving.

After all the water is turned off in the house, the dial on the meter should not move, or register usage. A water meter still moving, or registering usage, indicates you have some sort of a water leak inside the house. Water meters are also sometimes used to verify leaks after excavation work is done. To learn more read about Accurate Water Leak Testing By Using A Meter

Modern Water Meters

Most water meters in place now do not have leak dials, or any dials at all. Many, like the one pictured below all fully electronic. This particular meter actually has a solar panel, and the reading lights up when water is being used. Therefore, if the meter reading is lit up, you automatically know that water is running inside your house.


When water is running the reading lights up

How To Check If The Main Water Line Is Leaking

Frequently the 1st sign of a water main leak is not a drop in pressure, or water gushing up from the ground. In most cases the 1st sign of a water line leak is a rumbling or hissing sound on the pipes inside your house. This is typically most noticeable at night when your house is quiet. What follows are the three basic steps to check for a water line leak.

water line leak

Leaking Water Service Line

1. The first step involves closing the main control valve

To properly check for a leak on the main service line is to gently close the main control valve on the house side of the water meter. Always close the main control valve closest to the inside of the house, not the street side valve. That way if the valve breaks, you can still shut the water using the other valve, and repair it.

 2. The second step involves draining down the plumbing system

Drain down the plumbing inside the house by opening a plumbing fixture on the top floor and the lowest floor or basement.This is done to ensure that no residual water is running inside a toilet tank or from an underground pipe inside or under the house. Residual water would also make a sound on the pipes inside the house. This can confuse the source of the water leak.

Always check the condition and material of the inside plumbing. If galvanized pipe is present, never drain down the system. When galvanized pipe is drained, and then reactivated, blockages can form. If blockages form, there can be a loss of service. and

galvanized water pipes

Draining galvanized pipes was loosen corrosion and cause blockages

3. The third step involves “sounding out” for a leak

To check for a main water line leak requires listening to the line itself. Always try to listen as close to the point where it exits the house as possible. Ideally you should place your ear directly on the water main. If that is not possible get a small metal rod or screwdriver and place one end on the main water line and the other end on your ear.

Please note: There are specialty listening devices available, some are quite simple, others are very intricate and expensive. However, listening devices are are typically not necessary. If you think there is a chance you have a slight or undetected leak, you may be better to call a professional who has more experience in leak detection.

If no water is present or running inside the house plumbing there should be absolutely no sound on the water line itself. Any sound on the water line would indicate that the main water line is leaking outside the house. To also eliminate the possibility of a leak under the slab of the house (see below for more details), wait about 20 minutes, then listen again.

Checking For A ‘Running’ Toilet

There are two simple ways to check to see if a toilet is ‘running’. With no other plumbing fixtures running inside the house see if your water meter dial is ‘spinning’. Then close the valve under the toilet tank and see if the meter dial stops moving. If the meter dial stops moving you have a leaking and running toilet – you have found the problem.


Dye can be used to test for a running toilet

The 2nd way to check for a ‘running’ toilet is to place a small amount of food or clothing dye inside the toilet tank. After waiting about 10 minutes or so look in the toilet bowl and see if there is sign of the dye. If you see dye present you have a ‘running’ and defective toilet.

A running toilet frequently is audible and annoying. But it is also very costly – and even more annoying when you get your next water bill. The cost to repair a running toilet is less than the cost of water wasted in 1 year.

Signs Of A Water Line Leak Under Your Floor Or Slab

Leaks under a slab or basement floor are perhaps the most difficult to detect. Because they are usually not visible they are frequently misdiagnosed with resulting incorrect work orders and unnecessary aggravation. Testing for leak under a floor begins with some of the same steps mentioned above.

water line leak

Water Leak Under Floor

  • The 1st step is to see if your meter dial is spinning even though no water is being used inside the house. If it is proceed to the 2nd step.
  • The 2nd step as described above is to make sure you do not have a running toilet.
  • The 3rd step is to close the main control valve for the main water line as described above.
  • Then drain out the house plumbing as described above.
  • Lastly listen to the water main after waiting at least 10 minutes.

The reason the sound steadily decreases is that the residual water in the upper levels of house plumbing is slowly leaking out of the broken pipe under the floor. By taking the various steps described you have eliminated other possible sources of the leak such as a toilet or water main service line. If the main water line was leaking the sound on the piping would not go away, it would remain steady.

If you hear a sound of running water that steadily decreases, then disappears after you close the main control valve, it is likely that the leak is from a pipe under the floor or slab.

Testing For A House Sewer Leak

In some cases a leaking sewer joint can be mistaken for a leaking main water line. This can occur if the house sewer is in close proximity to the house water service line, and is also located above the finished grade of the basement floor. This is referred to in the trade as a “hung sewer”.

A leaking sewer joint near the outside of the foundation wall can result in water being present on the basement floor. Many times this type of sewer leak can look just like a water main break.main house trap

There is a definitive way to test for a sewer line leak outside the foundation wall. That is accomplished by doing a sewer dye test. A sewer dye test is performed by removing the cap from the house side of the sewer trap (click this link to learn about a sewer trap and the proper way to open it). Then place some food or clothing dye into the open sewer trap. The next step is to flush a toilet or run a sink for a few minutes to force the dye down the house sewer. For a fuller description of a sewer dye test read All About Sewer Dye Testing.

After waiting for no more than an hour if the source of the water leak is from the house sewer the dye will be visible on the basement floor or foundation wall.

Have A Further Inquiry Or Question?

Any questions or inquiries concerning any type of water main repair or sewer repair issue will be quickly addressed when you contact Balkan Plumbing. Joseph L. Balkan Inc. is dedicated to servicing and educating property owners when sewer and water main issues arise. Balkan Sewer And Water Main Service has been in continuous operation under the same trusted family name for well over 65 years.

No-obligation written estimates and free site visits are available day and night, seven days a week.

Get a free site visit today

Related articles about water line leak testing

About Balkan Sewer And Water Main Service

Balkan Plumbing is the largest and most trusted sewer & water main replacement company in NYC. We are licensed, bonded, and insured. Balkan is a family run business in continuous operation for over 65 years. Our 10 year unconditional guarantee on replacements means piece of mind for our valued customers. We are uniquely prepared to serve you due to our 48,000 square foot facility. In addition, we possess a fleet of trucks, heavy moving equipment, backhoes and pneumatics.

Choose Balkan Plumbing for your next subsurface plumbing issue. Whether a sewer repair, water main installation, water repair, or a water line leak. Balkan can correct DEP violations, and performs specialty work such as new sewer traps, backwater valves, hydrants, manholes, area drains, and trench drains.

Get free expert advice today

, , , , ,

angies list authority logo
bbb authority logo
queens jobsite mapbrooklyn jobsite mapmanhattan jobsite mapbronx jobsite map

Balkan Plumbing is the largest sewer and water main company in NYC. For over 60 years, our family's 10 year guarantee* means we stand by our work long after the job is done. For sewer and water main issues throughout Brooklyn, Queens, Manhattan, and the Bronx contact Joseph L. Balkan, Inc. today for 24/7/365 service. Paul R. Balkan, NYC Licensed Master Plumber 01281

Ph: (718) 849-0900 | Espanol (718) 943-5720 | Fx: (718) 849-9570