Blocked Drain or Hidden Leak? How to Tell

A blocked drain and a hidden leak can both cause damp, smells and stress, but they are opposite problems with opposite fixes. A blockage is water that cannot get away. A leak is water escaping where it should not. Knowing which one you have saves time and money, so here is how to tell a blocked drain from a hidden leak.

The simple difference

• A blocked drain means water will not drain away. It backs up, pools, or drains slowly. The water is in the right pipe, it just cannot move.
• A hidden leak means clean water (or sometimes waste) is escaping from a pipe inside a wall, under the slab or in the ceiling. The water is going where it should not.

They feel similar from the outside, but the clues are different.

Signs of a blocked drain

• Water draining slowly or pooling in the sink, shower or floor waste.
• Gurgling from drains or the toilet.
• A sewer or rotten-egg smell at the drain.
• Water backing up when you run the washing machine or flush.

If that sounds like your problem, start with our guide on how to clear a blocked drain.

Signs of a hidden leak

• A water bill that has jumped with no change in how much you use. This is the classic sign.
• Damp patches, bubbling paint or a musty smell on walls, ceilings or floors.
• The sound of running water when every tap is off.
• A warm spot on the floor, which points to a leak in a hot-water line under the slab.
• The water meter ticking over when nothing is running, turn everything off and watch it.

Why it matters which one it is

The fixes are completely different. A blockage needs clearing, with a jetter or a machine. A hidden leak needs locating and repairing before it wrecks your walls and floors, and the trick is finding it without tearing the house apart.

We use acoustic listening gear, thermal imaging and moisture meters to pinpoint a leak to the exact spot, so the repair is small and targeted. If you suspect water is escaping somewhere you cannot see, book a leak detection, the sooner it is found, the less damage it does.