Quick answer: what to check first
The most reliable early clues are an unexplained rise in your water bill, a water meter that keeps moving when everything is off, and damp, stained or musty areas near plumbing. No single sign proves a leak, but several together make one likely. The sections below group the signs by how you notice them, then explain how to confirm a leak and what to do next.
Signs you can see
- Stains on ceilings and walls. Yellow or brown patches, often with a darker ring at the edge, can mean water is reaching the surface from a pipe above or behind. After the leak is stopped, see how to fix a ceiling after a leak.
- Bubbling, peeling or blistering paint or wallpaper. Moisture behind a surface can push finishes off.
- Soft, warped or buckled flooring. Boards, laminate and vinyl may swell, lift or feel spongy where water is present (see how to repair water damaged floorboards).
- Cracks or discoloration in walls or flooring that are new and near plumbing. Cracks alone have many causes, so treat them as a clue rather than proof.
- Mold or mildew in places that stay damp, such as under sinks, in cabinets or along baseboards.
- Puddles or drips around fixtures, under sinks, near the water heater or at appliance connections.
- Corrosion on visible pipes and fittings, such as green or white crusty deposits on copper or brass joints.
Signs you can hear or smell
- The sound of running or dripping water when nothing is in use. A hiss near a wall or at the point where the supply enters the house is worth investigating.
- A musty or earthy smell that persists, especially in a basement, crawlspace or cabinet.
- Banging or whistling pipes are more often related to pressure or loose pipe supports than to leaks, but they are a reason to look closer at your plumbing.
Signs in your bills and water
- A higher bill with no change in use. Compare several months, keeping in mind seasonal watering and guests.
- Lower water pressure at several fixtures at once can indicate a leak, although sediment or a partly closed valve can also cause it (see how to fix low water pressure).
- Discolored or rusty water can point to corroding pipes. If it only appears briefly after water was shut off and turned back on, that can be normal. If it persists, have it looked at; light brown water from the faucet covers the common causes.
How to confirm a leak with the water meter test
- Turn off all water use inside and outside the house. That includes taps, showers, the washing machine, dishwasher, ice maker and irrigation.
- Find your water meter, usually in a box near the street or on an exterior wall or in a basement.
- Look at the small low-flow indicator (often a triangle or dial). Many meters show movement of this indicator even for very slow flow.
- Note the reading, wait 15 to 30 minutes without using water, and check again. If the indicator moved or the reading increased, water is escaping somewhere.
If it did move, close the main shutoff valve to the house and check the meter again. If the meter stops, the leak is likely inside the house. If it keeps moving, the leak may be in the buried line between the meter and the house. See what to do about a leaking water main for that case.
Toilets are a frequent quiet source of leaks. A few drops of food coloring in the tank, left for around 15 minutes without flushing, will show up in the bowl if the flapper is leaking.
How to tell whether a leak is behind a wall
Hidden leaks are harder to confirm. Helpful steps:
- Look for the signs above clustered along one wall, especially near a bathroom, kitchen or water heater.
- Feel for cool, damp spots and check whether they get worse after using nearby fixtures.
- Use a moisture meter if you have one, comparing readings against a dry wall nearby.
- Use a thermal imaging camera or acoustic listening device if you can borrow or rent one. Results can be ambiguous, so treat them as pointers.
Avoid cutting into walls near wiring until you are confident where the pipes run. If you are unsure, a plumber or leak detection specialist can pinpoint the leak with less damage.
How long can a leak go unnoticed?
A slow leak inside a wall, under a floor or underground can run for weeks, months or longer because there may be nothing visible. The harm tends to build gradually, through rot, mold and higher bills. That is why a periodic meter check, especially after an unexplained bill increase, is worthwhile.
Common sources of leaks
There is no single answer to the most common leak, but the usual suspects are:
- Dripping faucets and worn washers or cartridges (see how much water a dripping faucet wastes)
- Toilet flappers and fill valves (see toilet tank leaking water into the bowl)
- Supply lines and connectors under sinks and behind appliances (see how to find and fix a leak under the sink)
- Pipe joints and fittings
- Aging or corroded pipes, depending on the material (see copper vs plastic water pipe)
- Water heater connections and relief valves (see water heater tank leaking from the bottom)
- The underground service line
What to do if you suspect a leak
- Shut off the water to the affected fixture, or at the main shutoff if you cannot tell where it is coming from. Know where your main shutoff is before you need it.
- Stay safe around electricity. If water is near outlets, light fixtures, appliances or a breaker panel, or is dripping through a ceiling with lights on, switch off power to that area at the breaker only if you can do so safely without standing in water. If in doubt, stay out and call an electrician or your utility.
- Limit the damage. Mop up standing water, move belongings, and run fans to dry the area.
- Take photos for your records in case you make an insurance claim.
- Call a licensed plumber for leaks inside walls, behind or under floors, in a main line, or whenever the source is unclear.
- Treat mold and old materials with care. Large areas of mold, or water damage to materials in an older home such as insulation or flooring that could contain asbestos, should be assessed by a qualified professional before you disturb them.
If a pipe is failing widely, with repeated leaks in different spots, ask a plumber about replumbing a house rather than repairing one leak at a time.