The water bill that crept: finding a hidden leak with one quiet hour and the meter

A bill that creeps upward while usage stays honest is a leak that outgrew its hiding place - and unlike most plumbing, a hidden leak rewards method over money: one quiet hour with the meter, a torch and a tablet of food colouring finds the majority of them. This guide is the method.

The meter test - the whole argument in two numbers

Everything off: taps closed, the dispenser's pump off, the washing machine mid-cycle skipped, the toilet's cisterns left alone to complete their refills. Find the meter's small triangle or low-flow indicator - it turns with a dribble nobody can see - and if it moves with nothing open, the house is leaking; note the reading, wait the full hour with nothing opened (that hour is the test's price), and note it again. The delta is the leak's flow rate per hour, and the desk's rough categories for what it means: a tenth of a cubic metre over the hour is a weeping cistern's number - a third is a running toilet's, and a whole cubic metre is a pipe or a tank's, and the hunt below should feel urgent at those numbers. The one false positive worth naming: a pressure tank or an inverted-house tank's auto-fill cycling counts as flow - shut that valve for the hour too, or subtract its share.

The quiet hunters, by where leaks hide

• The toilets: food colouring into each cistern, no flush, ten minutes, and colour in any bowl is that toilet's flapper - the cistern chapter's twenty-minute fix. This single check causes more meter deltas than everything else combined.
• The under-sink and behind-appliance runs: a dry paper towel along each joint, left an hour, reads a damp line where fingers miss it - the soft-hose braids and the bottle traps are where the slow stains on cabinet floors start.
• Under floors and inside walls, the floor-tile test: a hollow tile with a damp grout line, or the patch of cool that keeps a mop from drying normally, points below - the concrete slab carries a leak sideways, and the sound of a whisper of running water with every tap shut in a quiet house is the underground leak's own confession. Mark the spot and let it become a plumber's exact address instead of their opening guess.
• The external taps and the tank: a tap's spindle washer drips into the wall instead of the sink and never shows, and the header tank's overflow pipe is the least-loved metre of pipe in any house - the float valve on a tank is this guide's flapper.

The line where DIY stops

A meter that turns with everything shut and the room-by-room hunt that keeps pointing inside a wall or under a slab is the leak-detection specialist's day job - they bring acoustic correlators and thermal cameras and, for what a week's water bill plus a month's damp costs, hiring them is the cheap option; the desk's addition: hand over the two numbers you measured. An hour of method that turns "I think there's a leak somewhere" into "the north wall, between the bathroom and the kitchen" is the discount the professional's invoice gives back.