Most of the water damage we remediate was discovered late. Not because the homeowner was careless, but because the early signals of a concealed leak are subtle, easy to rationalize, and rarely look like water at all.
1. A musty smell with no visible source
That earthy odour is microbial volatile organic compounds — gases produced by active mould growth. They pass through drywall long before spores do, which means you will reliably smell a wall cavity problem months before you can see it. If a closed room smells musty when you open it, there is moisture somewhere in that assembly.
2. A water bill that moved without you
Compare against the same month last year rather than last month. A jump of a few thousand gallons with no change in household usage is a leak, and if you cannot see it, it is under the slab or inside a wall. Confirm by shutting every fixture and watching whether the meter's low-flow indicator still turns.
3. Running water you can hear but not find
Turn everything off, wait for the house to settle, and listen at quiet times. A faint hiss or trickle inside a wall or beneath the floor is a pressurized supply leak. In slab homes this is the classic slab leak signature, often paired with an unexplained warm spot on the floor.
4. Paint or wallpaper that has stopped lying flat
Bubbling, blistering, peeling at seams or a faint chalky bloom all indicate moisture moving through the substrate from behind. Paint fails from the back long before it fails from the front.
5. Floors that changed shape
Hardwood cupping at the board edges, laminate swelling at the seams, tile that has developed a hollow sound, or vinyl lifting at the perimeter — all indicate moisture in the subfloor beneath. Cupping in particular means the underside of the board is wetter than the top.
6. Nail pops and hairline ceiling cracks
Drywall that repeatedly pops fasteners or cracks in the same place is moving, and moisture cycling is a common reason. On a ceiling directly below a bathroom or attic air handler, treat it as a leak until proven otherwise.
7. Symptoms that follow the building
Congestion, headaches, itchy eyes or a cough that improves within a few hours of leaving the house and returns when you come back is the most reliable non-instrument indicator of an indoor mould problem there is. Pay particular attention if only some family members are affected — sensitivity varies widely.
8. Condensation where there did not used to be any
Persistent window condensation, sweating pipes, or damp patches on interior walls indicate indoor humidity above the comfortable range. Buy a $15 hygrometer. Anything consistently above 55% relative humidity is feeding mould whether or not you have a leak.
9. Discolouration that keeps coming back after painting
A stain that reappears through fresh paint is not a stain, it is an active leak. Tannins and minerals are being carried through the substrate by ongoing moisture movement. Sealing over it changes nothing except how long it takes you to notice.