A water meter measures flow, not intention
The impeller inside turns when water moves and stops when it doesn't. It has no idea whether anyone wanted the water. So the question "is there a leak?" has an exact, free, five-minute answer that most people never collect — and instead jump straight to "the meter must be faulty" or "I'll just pay it".
The reason the bill is the first thing anyone notices is that bills arrive every two or three months. A leak can run invisibly on paper for that entire period. By the time the number looks wrong, tens of cubic metres have already gone through. A toilet with a seeping flapper loses one to three tonnes a day — and it is completely silent, because the water runs down the inside of the pan where you never look.
Three forms of movement, three different answers
- It turns steadily, one direction — the leak indicator (a small red triangle or star on a mechanical meter, a pulse light on a smart one) rotates at a constant speed with everything off. That is a real leak: continuous, unidirectional flow. Turn everything off, photograph the reading, wait, re-read, and work out the rate.
- It swings back and forth, unevenly — fast, slow, forward, backward, never settling. That is not a leak. Trapped air in the pipes expands and contracts as mains pressure varies and pushes the impeller both ways. A failed check valve does the same thing. Bleed the air at a tap, re-test; if it persists, check the check valve.
- It creeps, almost imperceptibly — one minute shows nothing, but thirty minutes moves the red digits one place. That is a small leak, and the overwhelming favourite is a toilet. Isolate the fixtures one at a time until the meter stops.
The arithmetic that changes the decision
People dismiss small leaks because a drip feels trivial. Convert it and it stops feeling trivial. Take your rate in litres per minute, multiply by 1440 for litres per day, then by 365 and divide by 1000 for cubic metres per year. In the picture the calculator shows the benchmark case: 0.5 L/min looks like a thin trickle you cannot even hear, and it is 720 litres a day — 263 cubic metres a year. A one-litre-per-minute leak is over 500 m³. That is the number worth acting on, and you measured it for free.
Isolate before you call anyone
Shut the valve after the meter and watch: if the indicator still turns, the leak is on the supply side or between meter and valve — usually the utility's problem, so report it. If it stops, open that valve, shut the garden or irrigation branch, and watch again: turning means the outside line or irrigation. If that stops it too, open the garden and shut the valve into the house — turning means it is indoors, and you have just saved a call-out fee by proving it. Then work room by room on the isolating valves. Listening helps once you are close: at night, with everything off, put one end of a wooden stick or a screwdriver against the wall or floor and your ear to the other. A leak is a continuous high hiss. Check bends, joints, and anywhere the wall is damp, blistering or mouldy.