A slow leak behind a wall or under a slab can waste thousands of litres and cause real damage before you ever see water. Here's how to spot one early.
Not every leak announces itself with a puddle on the floor. The expensive ones hide — behind a wall, under a slab, or in a ceiling you never look at — and by the time you see water, the damage is done. Here are five signs that say you've got a hidden leak.
1. Your water bill jumped with no explanation
This is the most common first clue. If your usage hasn't changed but the bill climbed 20% or more, water is going somewhere it shouldn't. Compare a few recent bills — a single spike could be a one-off, but a steady climb points to an ongoing leak.
2. The sound of running water when nothing's on
Sit quietly in the house with all fixtures off and listen. A faint hiss, dripping, or the sound of water moving through pipes when nothing is running often means a leak in a supply line or a running toilet. Toilets are the sneakiest — a slow flapper leak can waste hundreds of litres a day and you'll barely hear it.
The dye test is quick: drop a few drops of food colouring in the toilet tank, wait 15 minutes, and see if colour shows up in the bowl without flushing. If it does, the flapper is leaking.
3. Damp, warm, or stained spots on walls, floors, or ceilings
A wall that's soft or discoloured, a warm spot on the floor, or ceiling paint that's bubbling or peeling are all classic behind-the-wall leak signs. Warm spots, in particular, often mean a hot-water supply line has failed inside the wall. Don't ignore a musty smell either — that's moisture feeding mould you can't see.
4. Low water pressure or a sudden drop
If pressure drops at one fixture, it's usually a clogged aerator. If it drops across the whole house, you may have a leak in the main supply line. A leak between the meter and the house wastes water you're paying for but never using — and in older neighbourhoods with galvanized or polybutylene lines, main-line failures aren't rare.
5. Cracks in the foundation or unexplained puddles outside
Leaks under a slab or in a buried line can erode soil beneath the foundation, leading to cracks that appear with no other explanation. Puddles or unusually green, lush patches in the yard when it hasn't rained are the above-ground version of the same problem.
What to do if you suspect a leak
Start with the meter. Turn off every fixture in the house and check the water meter — if the low-flow indicator (often a small triangle or gear) is still spinning, water is moving somewhere. Then shut the main valve inside and check again; if the meter stops, the leak is inside the house.
For hidden leaks, we use acoustic and thermal detection plus camera inspection to find the source without tearing into walls blindly. The goal is always to pinpoint the leak first — then repair surgically, not guess-and-cut.
If any of these signs sound familiar, don't wait. A leak that costs a few dollars today in wasted water can cost thousands in drywall, flooring, and mould remediation next month.
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