A damp patch on the ceiling. A musty smell that won't shift. A skirting board starting to swell. You know water is escaping somewhere in the bathroom, but where? The shower is the usual suspect, and often guilty, but it's far from the only candidate. And because water travels along surfaces before it shows itself, the damp patch is frequently nowhere near the actual leak.
Guessing wrong is expensive: you pay to fix the wrong thing while the real leak keeps working. Here's how to narrow it down, and how professionals confirm it.
The usual suspects, by symptom
Damp ceiling below an upstairs bathroom: most often the shower base, a drain connection, or waterproofing that has failed under the floor tiles.
Mould or musty smells that survive every clean: moisture trapped behind tiles or under flooring, typically from failed grout or seals letting water through a little at a time.
Water pooling near the toilet or vanity base: worn seals around the pan collar or cistern, or perished silicone around the vanity. These leaks can be silent for months.
Bubbling paint or swollen timber near the shower: water escaping through the screen joins, wall junctions or grout lines beside the shower.
White residue (efflorescence) on tiles: water has been seeping beneath the tiles and carrying minerals back to the surface.
Hollow-sounding or cracked tiles: often a sign of water movement underneath, lifting tiles from their bed.
Self-checks you can do this weekend
Test the shower base. Plug the drain and fill the base using water from another tap: a bucket or a hose from elsewhere in the house. If you fill it from the shower itself you can't tell whether the base or the plumbing is leaking. Watch the base and the surrounding area (and the ceiling below, if there is one) for any sign of escape.
Test the screen. Dry everything, then direct the shower head or a hose at the joins between the screen and the walls. Seepage here means the screen seals, not the waterproofing, are your problem.
Inspect the surfaces. Work along grout lines, tile edges and silicone joints looking for cracks, gaps, missing grout and hairline tile fractures. Check taps, mixers and visible drain connections for drips and loose fittings.
Rule out the bath and basin. Fill, hold, and release, watching underneath and behind while you do.
If a self-check finds the culprit and it's a single failed seal, you're ahead. But be careful with the conclusion: finding a problem isn't proof it's the problem, and water may still be concealed behind tiles.
When it's time for professional detection
Call in professional leak detection when:
- The self-checks come back clean but the damp keeps appearing
- Water shows up in a room next to or below the bathroom
- A previous "fix" didn't stop it
- You need the source documented, for an owner, an agent, a strata committee or an insurer
Professional detection replaces guesswork with evidence: dye flood testing traces exactly where water escapes, thermal imaging shows moisture behind walls and under floors without opening anything, pipe pressure testing confirms or rules out the plumbing, and moisture readings map how far water has travelled. You get a written report with photos and a scope of works to fix what was found, so the repair, whether it's sealing the shower or a plumber's job, targets the real source.
Why speed matters
Constant damp doesn't just feed mould. It rots timber, wicks into wall cavities, damages the rooms around and below the bathroom, and damp timber attracts termites, a headache no Sydney homeowner needs. A leak found this month is a sealing job; the same leak found in two years can be a renovation.
Stop guessing. SmartSealed's leak detection pinpoints the source: dye testing, thermal imaging, pressure testing and a written report with photos. 30+ years across Greater Sydney.