How to Diagnose a Water Leak in Your Home—and Why You Should Do It Before You Call the Plumber

Get your wrenches ready. Finding and fixing many common plumbing leaks just may be easier than you think.

If you suspect a hidden leak, your water meter has just become your best friend. Roman Zaiets/Shutterstock

Leaky pipes increase your water bill, may cause structural damage, and can lead to mold and its ensuing Pandora’s box of complications. The good news is that suspecting you have a leak means you’re already on your way to fixing the problem.

There are two types of leaks: visible—such as water puddling beneath a sink, possibly due to a loose drain joint—and hidden. If you suspect a hidden leak, your water meter has just become your best friend. Even if you ultimately end up calling a plumber, by following the tips below you’ll be able to save him some time and, in turn, save yourself money.

Meter Diagnosis

Water meters are commonly found near the street, typically under a manhole-style cover. Ideally, you should have a water meter key, available at any hardware store, to open the manhole cover and turn the water supply on and off. If you don’t, an oversized screwdriver will open most covers, and pliers and some elbow grease will control the water supply.

If you notice the surrounding grass is particularly green and lush, or the water meter box is filled with water, and it hasn’t rained recently, you may have just found that the problem is at the meter. But don’t close up the meter box just yet; you’ll still want to check inside.

Further Exploration

Turn off all the faucets, the washing machine, and the dishwasher. Make sure the landscape sprinkler system, if you have one, is not on, and no one is using an exterior hose. If the meter is still moving, you have a leak. A stopped meter, however, doesn’t mean that you don’t have a leak. Note the numbers, then come back an hour or two later. Have the numbers moved?

Note that a water meter will not show a leak on the municipal supply side, so if the numbers haven’t changed, but you still have low water pressure or you notice the aforementioned lush lawn around the meter, you may want to reach out to your town or city.

The majority of plumbing leaks happen at connection points. Use a flashlight to check and, if necessary, tighten or replace them.
Lenar Nigmatullin/Shutterstock

Investigate the Connections

The majority of plumbing leaks happen at connection points. Use a flashlight to check the faucets, the drain pipes under the sinks, as well as the connections for the washing machine, refrigerator, dishwasher, water heater, water filtration system, shut-off valves, and toilets. The fix may be as simple as tightening a connection or replacing a worn-out washer or a failing supply line hose. Also check the appliances and fixtures themselves to determine if they have internal leaks.

In the case of a leaking faucet due to a failed O-ring or washer, you probably can either fix it or replace it yourself. Check the warranty first to make sure you don’t inadvertently void it.

As for water heaters and appliances, if they’re out of warranty and you feel confident in your mechanical skills, check online to see if you can get a PDF of the service manual for your unit. Service manuals are made for technicians and go far beyond the one that came with the appliance, providing a wealth of useful information.

Toilet Test

If all the faucet and appliance connections are dry, it’s time to turn your attention to the toilet. If the porcelain throne is randomly flushing, it’s most likely caused by the toilet flapper—the rubber part that opens and closes each time you flush it.

A slow leak is harder to diagnose. Put a drop of food coloring in the tank; if the seal is faulty, the dye will appear in the bowl within 30 minutes.

The Flapper

Toilet flappers age and accumulate mineral build-up. The fix may be as simple as cleaning it. If not, it’s an easy change-out project with parts available at most home supply stores.

Turn off the water supply to the toilet, or the whole house if there’s no toilet shut-off in the bathroom. Flush the toilet until it’s empty, then unclip the flapper from the flush chain and pull up on the flapper to remove it from its posts. To install a new one, simply reverse the process.

Kohler AquaPiston and some American Standard turbo flush toilets use a round seal that goes on the bottom of the canister valve assembly. Refer to the manual to change them.

The Fill Valve

The toilet fill valve, the tall piece where the water comes into the reservoir tank, is another potential source of a leak. These are under a lot of pressure and can begin to leak over time.

Turn off the water supply, flush the toilet until the tank is empty, and then unscrew the black, red, or yellow stop cap at the top of the fill valve, turning it in the counterclockwise direction. If the fill seal looks worn, replace it.

If you decide to change out the entire fill valve, first put a bucket under the incoming water line underneath the tank before removing the water supply line. Remove the supply tube—the short, small hose—connected to the valve inside the tank, unscrew the fill valve, and remove and replace the parts in reverse order.

If you’ve checked everything above and still have a water leak, it’s probably time to call in a leak detection service.

SIDEBAR: Pipe Noises

You don’t have ghosts; the scary noise coming from your wall is the plumbing system talking to you. Here’s how to decode its language.

Banging

Water hammers occur when a valve is shut off suddenly. It is a sign of air in the lines. Shut off the water main and open your faucets to drain the system and the air. Turn the water back on. If that doesn’t work, you’ll need a water hammer arrestor installed.

Whining/Vibration

If your pipes sound like something out of a Stephen King novel, your water pressure may be too high. Get an inexpensive water pressure gauge and connect it to an outside spigot. If your pressure is over 80 psi, you’ll need to have a pressure regulator installed.

Whistling/Squealing

When pipes begin to make a high-pitched noise, it’s a clue that a shut-off valve washer is wearing out. Your ears are all the tools you need; check the valves beneath the toilets, sinks, etc. Replace the entire valve; if it’s welded on, you’ll need a plumber.