Leak Detection: Finding Hidden Water Leaks Before They Cause Damage

Not every leak announces itself with a puddle. Slow leaks inside walls, under floors, or in buried lines can run for months, raising water bills and causing mold and rot. Catching them early is far cheaper than repairing the damage later.

Warning signs of a hidden leak

• An unexplained increase in your water bill.
• The sound of running water when nothing is on.
• Stains, bubbling paint, or soft spots on ceilings and walls.
• Musty odors or visible mold.
• Warped or lifting flooring.
• Lower water pressure than usual.
• Warm spots on the floor, which can indicate a hot water leak under a slab.
• Cracks in the foundation or wet spots in the yard.

A simple meter test

You can check for leaks yourself with the water meter:

1. Turn off all water fixtures and appliances inside and out.
2. Find your meter and note the reading or watch the leak indicator, a small dial or triangle on many meters.
3. Wait 15 to 30 minutes without using any water.
4. Check the meter again. If it moved, water is going somewhere.

To narrow it down, close the main shutoff valve inside the building. If the meter still moves, the leak may be on the service line between the meter and the building. If it stops, the leak is inside.

In New York City, DEP customers with wireless meters can monitor usage through their online account and sign up for leak alerts. On Long Island, check with your water supplier about usage tools.

Common leak sources

• Toilets. A worn flapper can let water run silently into the bowl. Add a few drops of food coloring to the tank; if color appears in the bowl without flushing, the flapper needs replacing.
• Faucets and shower valves. Drips add up over time.
• Supply lines to sinks, toilets, and appliances, especially old braided hoses.
• Water heaters, including relief valves and tank failures.
• Washing machine hoses. Rubber hoses can burst; braided stainless hoses are a common upgrade.
• Dishwasher and refrigerator ice-maker lines.
• Boiler systems, where a slow leak may show up as frequent pressure drops or automatic refilling.
• Shower pans and tile that let water seep into the floor or ceiling below.
• Drain lines that leak only when a fixture is used.

How professionals find leaks

When the source is not obvious, plumbers and leak specialists use several methods:

• Pressure testing sections of piping to isolate where pressure is lost.
• Acoustic listening devices that pick up the sound of escaping water through walls, floors, and soil.
• Thermal imaging to spot temperature differences caused by water, especially hot water lines.
• Moisture meters to map wet areas in walls and floors.
• Camera inspection for drain and sewer lines.

The goal is to find the leak with as little opening of walls and floors as possible.

Leaks in apartments and multifamily buildings

In multifamily buildings, a leak in one unit often shows up in the unit below. Finding the source may require access to several apartments and the risers. Building owners and managers should respond quickly to reports, because leaks can spread and cause mold, and in NYC, unresolved leaks and mold can lead to HPD violations.

Preventing leaks

• Replace washing machine hoses and old supply lines proactively.
• Install shutoff valves that work at every fixture.
• Consider automatic leak detectors or shutoff systems, which sense water and alert you or close a valve.
• Keep gutters and grading directing water away from the foundation.
• Address small drips and running toilets promptly.
• Have older piping evaluated during renovations.

When to call for help

Call a plumber if the meter test shows a leak you cannot find, if you see water damage spreading, or if you suspect a leak in a wall, slab, or buried line. The sooner a leak is found, the less damage there is to repair.

From prewar apartment buildings in Manhattan to homes in Suffolk County, water leaks are one of the most common causes of property damage, and one of the most preventable.

This article is general information for property owners, not legal or engineering advice. Rules and procedures change; confirm current requirements with the agency or utility involved.