A hidden leak is water escaping somewhere you cannot see it, such as inside a wall or floor void, beneath a slab, or on a buried supply line. The escaping water is rarely the first sign. Rising water use, a faint running sound, or a floor that never quite feels dry usually come first.
Start with the meter
The water meter is the most reliable leak detector already installed at the property. Close every tap, stop appliances mid-cycle, and make sure no toilet is refilling. Note the meter reading, wait an hour without using water, and read it again.
If the reading has moved, water is leaving the system somewhere. Many meters also have a small leak indicator dial or triangle that rotates on very low flow, which is a useful check when a leak is too slow to shift the main digits quickly.
Split inside from outside
Close the main isolation valve where it enters the building, then repeat the meter test. If the meter still moves, the loss is upstream of that valve, on the supply run before the building. If it stops, the leak is inside.
Rule out the usual suspects
- A toilet fill valve that tops up silently. Add a few drops of food colouring to the cistern and check whether colour reaches the bowl without flushing.
- An outdoor tap or irrigation line that runs on a timer.
- A pressure relief discharge from a water heater that drips into a drain out of sight.
- A softener or filter unit that regenerates on a schedule.
Signs worth taking seriously
- A warm patch on a floor over a slab, which can indicate a hot water line below.
- Paint blistering, plaster staining or skirting boards separating in one recurring spot.
- A musty smell in a cupboard or room that persists after ventilation.
- The sound of running water when everything is closed.
What to record before you call
Note the meter readings and the times you took them, whether the loss continued with the main valve closed, where any damp appears and whether it changes with use. That information turns a broad search into a targeted one and shortens the detection work considerably.
If water is escaping visibly, close the main isolation valve first. Knowing where that valve is, and that it still turns, is the single most useful piece of plumbing knowledge in any building.
Need this looked at rather than explained?
Submit a service request describing what you have observed. Details like when it started and which fixtures are involved shorten the diagnosis considerably.
Request service