Leak detection, for water you can see the damage from but not the source
A bill that climbed for no reason, a damp patch that keeps coming back, or a musty smell in a room nobody uses. Hidden leaks are usually found by narrowing them down rather than by guessing, and there is a test you can run yourself tonight that will tell you whether you have one at all.
The meter test settles it in an hour
Before anyone charges you to look for a leak, it is worth establishing that one exists. This costs nothing and takes about a minute of actual effort.
Water meter test
Works on any house on municipal water with an accessible meter.
- Turn off everything that uses water. Taps, dishwasher, washing machine, ice maker and irrigation. Ask everyone in the house not to run anything.
- Find the meter and note the reading. Photograph it, including the small sweep hand or leak indicator dial if it has one.
- Leave it strictly alone for one to two hours. No flushing, no hand washing. This is the part people get wrong.
- Read it again and compare against the photograph.
If your leak indicator dial is spinning while everything is off, you can stop here. That is a leak, and you do not need to wait the hour.
What each symptom usually points at
Leaks announce themselves differently depending on where they are. These are the patterns we see most often here.
| What you are seeing | Where it usually comes from |
|---|---|
| Bill up, nothing visible anywhere | Most often a toilet leaking silently into the bowl, which is both the commonest cause and the cheapest fix. After that, a supply line under a slab or in a wall. |
| Warm patch on a floor | A hot water line running under the floor, or a leak in radiant heating tubing. Worth taking seriously in a house with radiant heat, because it is a heating problem as well as a plumbing one. |
| Damp patch that returns after drying | An active leak rather than a past event. Water tracks along framing, so the wet spot is frequently some distance from the actual source. |
| Musty smell, no visible water | Something wetting a concealed cavity, often slowly and for a long time. The smell usually arrives well before any stain does. |
| Stain on a ceiling | A fixture, drain or supply line on the floor above, or a roof issue rather than plumbing. Establishing which comes first, because they are different trades. |
| Sound of running water with nothing on | A supply leak somewhere under pressure. This one tends to be larger than average, since you can hear it. |
| Pressure dropped across the house | Corroded galvanized supply lines, which are still in plenty of older housing here, or a leak on the service line before it reaches the house. |
| Boiler losing pressure repeatedly | A leak somewhere in the heating loop, which may be a fitting, a failed expansion tank, or buried pipework. It is topping itself up and the water is going somewhere. |
Test your toilets before booking anything. Put a few drops of food coloring in the tank, leave it thirty minutes without flushing, then look in the bowl. Color in the bowl means the flapper is leaking and that is your bill. It is the single most common hidden leak in any house, it makes no sound, and the part costs very little.
Narrowing it down before opening anything
The point of leak detection is to open one small area rather than several large ones. That is a process of elimination more than it is a gadget.
- Confirm there is a leak at all. The meter test, repeated under controlled conditions. Surprisingly often the answer is a toilet, an irrigation zone, or a bill estimated rather than read.
- Separate supply from drain. A supply leak runs constantly under pressure. A drain leak only appears when something is used. Knowing which changes where we look and what we test.
- Isolate by section. Shutting off zones of the house in turn and rerunning the meter narrows a whole building down to a branch, without touching a wall.
- Pressure test the suspect section. Isolating a run and watching whether it holds pressure confirms the branch before anything is opened up.
- Locate within the section. This is where non-invasive tools earn their keep, including moisture meters and thermal imaging on hot lines, which show temperature patterns through a floor or wall.
- Open one place, once. The whole exercise is about the last step being small and correct rather than exploratory.
Why we would rather find it than guess. Speculative cutting is cheap for us and expensive for you, because you pay to repair every hole whether or not the leak was behind it. Time spent narrowing is almost always cheaper than drywall.
Leak detection questions
Tell us what you are seeing
What the symptom is, roughly when it started, and whether you have run the meter test. If you have a reading from before and after, include both, because it saves us repeating it.
Next steps and neighbors
Find it before it finds your drywall
Run the meter test tonight, check your toilets with food coloring, and call us with what you found. Half the time that is the whole answer.