The single most common reason a leak repair fails is that it was carried out where the water appeared.
It is an entirely reasonable assumption. There is a stain on the ceiling, so something above it must be leaking. Someone re-seals what is above it, the stain is painted over, and four months later — usually after a decent stretch of driving rain — it comes back slightly larger than before.
The assumption is wrong because water inside a building does not fall straight down. It travels.
Water follows the path of least resistance
Once water gets past the outer surface of a building it moves through whatever route offers least resistance, and that route is decided by the construction, not by gravity alone.
Along the top of a slab. A concrete slab is rarely dead level, and a waterproofing membrane laid over it creates a plane that water can run along for metres. Water entering at a failed upturn on a balcony can travel back into the building and emerge at a doorway, a wall junction, or the edge of a slab several rooms away.
Down the cavity face of a stud wall. Water that gets behind cladding runs down the inside face of the frame. It will pass three floors without a trace if nothing interrupts it, then wet a bottom plate or a window head where a noggin or a piece of insulation catches it.
Across a suspended slab into the unit below. In multi-residential buildings, water that gets under the tiles of one balcony frequently ends up on the soffit of the balcony below — sometimes not the one immediately underneath.
Along services. Conduits, pipe penetrations and cable trays are effectively channels through the structure. Water finds them, runs along them, and appears wherever they terminate.
Through capillary action, upward. Water rises in porous materials against gravity. Rising damp in a wall base and wicking up through a screed both work this way, which is why a stain can appear above the level water entered at.
The practical consequence is simple: the visible damage marks the point where water stopped moving and started evaporating. That point may be centimetres from the defect, or it may be twenty metres and two storeys away.
Why timing misleads as well as location
Owners naturally connect a leak to rain, and often to a particular event — a storm, a burst hose, an overflowing gutter. That connection can be just as misleading as the location.
Water held in a screed, an insulation layer or a slab does not release quickly. A defect that only admits water in wind-driven rain from one direction may deposit water that keeps a ceiling damp for weeks afterwards. By the time the stain appears, the weather that caused it has long passed and the sky is clear.
Equally, a leak that seems to happen "only when it rains" is not necessarily a rain leak. A shower used every morning produces a stain on a schedule that looks weather-independent, while a slow plumbing leak produces a stain that never dries out at all. Constant dampness usually means plumbing. Dampness that comes and goes usually means ingress. That distinction is one of the first things a survey establishes, and it changes who fixes the problem.
What this means for repairs
Three failure patterns follow directly from chasing the stain.
The repair is in the wrong place. Silicone goes around the shower screen when the water is entering at a failed puddle flange under the tiles.
The repair is too small. A single crack is patched when the membrane behind it has debonded across a whole balcony, and the water simply finds the next weakest point.
The repair addresses a symptom of something structural. Sealing a crack that is opening because of slab movement buys a season, because the crack will open again.
Every one of those ends with the owner paying twice — and in a strata building, usually with an argument about who pays in between.
What a proper investigation does instead
A leak investigation is a process of elimination that works from the visible damage backwards to a source, without cutting the building open to find out.
Establish the moisture extent, not just the wet patch. The visible stain is a fraction of the affected area. Infrared thermography reveals the thermal pattern of evaporative cooling across a whole ceiling or wall, showing how far the moisture actually reaches. That pattern usually points in a direction.
Measure moisture through the build-up, not at the surface. Knowing that a surface is damp is not useful. Knowing whether the water is in the tile bed, the screed or the slab beneath it decides the entire scope of a repair. Microwave reflection moisture mapping reads moisture at depth, layer by layer, without breaking anything.
Test one variable at a time. Flood testing a balcony with the drainage blocked, running a shower with the waste sealed, or wetting one façade section at a time isolates which element is admitting water. A leak that stops when one element is taken out of the equation has been found.
Look at the outside as well as the inside. Where the source is a façade, a balustrade fixing, a parapet or a roof detail, it has to be inspected at close range. On a high-rise that means rope access, which puts a technician's hands on the actual joint rather than a pair of binoculars on it from the ground.
Rule out plumbing. Pressure testing supply lines and camera-inspecting waste lines separates a services failure from a building fabric failure. These have different causes, different repairs and — in strata — different people responsible.
The report matters as much as the finding
In a body corporate or an insurance context, a leak investigation that ends in a verbal opinion is worth very little. What is needed is a document that records the moisture distribution, the tests carried out, what each one eliminated, and the conclusion those tests support.
That report is what allows a committee to approve a scope of work, an insurer to assess a claim, or a builder to be held to a warranty obligation. It is also what prevents the same investigation being paid for twice by two different parties.
The short version
The stain is evidence, not a location. Repairing where water appears is a coin toss, and it is a coin toss the owner pays for either way.
If you have a leak that has already been repaired once and come back, that recurrence is itself diagnostic: it usually means the first repair addressed a symptom. Tell us where it shows up and when, and we will tell you which method will find it.