Professional leak detection finds where water is coming from before anything is opened up. The stain on your ceiling is where the water ends up, not where it starts — water can travel along a slab, a pipe sleeve or under a membrane for metres before it shows. Finding the true source first is what stops you paying to fix the wrong thing.
Here is how each method works, and what it can and can't tell you.
1. Visual survey and history
The first tool is questions. When does it leak — after rain, after showers, or all the time? Is the stain growing? What is directly above it, and what is above that? The pattern alone often narrows the source down to one or two possibilities.
2. Moisture mapping
A moisture meter reads how wet a wall, floor or ceiling is at each point. Taking readings in a grid builds a map of where it is wettest — and the source is usually at the wet end of that map, not under the visible stain.
3. Thermal imaging
An infrared camera shows surface temperature. Wet materials are typically cooler as the water evaporates, so a thermal image reveals the shape of a damp area and often the path the water is taking. It is fast and non-destructive, but it is always confirmed with moisture readings, because other things (an AC duct, a cold pipe) also show up cool.
4. Pipe pressure testing
Hot and cold supply lines are isolated and pressurised, then watched. If the pressure drops, there is a leak in that line. This is the test that separates a pipe leak from a waterproofing leak — and it is why we never quote to retile a bathroom before doing it. See our guide on bathroom leaks into the flat below.
5. Dye and flood tests
For showers, drains, roofs, terraces and pools, a coloured dye or a controlled flood shows exactly which area lets water through. A roof or terrace can be dammed and flooded to recreate heavy rain; a shower can be tested on its own while the ceiling below is watched.
What leak detection can't do
No method sees through concrete like an X-ray. Detection gives a confirmed source in most cases, and a most-likely source in the rest. A good report says which it is, and why.
What a good leak report includes
- Photos and thermal images
- Moisture readings and where they were taken
- Every test carried out and its result
- The confirmed (or most likely) source
- The recommended repair
That report is also your evidence if the leak is coming from a neighbour's unit, a common pipe or a new building still within its defects period.
Then what?
Most leaks we find turn out to be waterproofing failures — a bathroom, a roof, a terrace or a pool. With the source confirmed, the repair can be quoted as one fixed price, done once and flood-tested. Book leak detection to start.