01 Sept 2026
The bill arrives, the water figure is far higher than last time, and nothing about how you live has changed. Before you assume the worst, work through it in order. Some of these have an ordinary explanation, and the ones that do not are worth catching quickly.
Read the bill in cubic metres, not dollars
The dollar total moves for reasons that have nothing to do with your plumbing. Find the volume of water used, in cubic metres, and compare that figure against the same figure on your previous bills. If the volume is flat and only the money moved, you do not have a leak.
Then check whether the reading was an actual meter reading or an estimate. Where a meter could not be read, the account is estimated, and the next actual reading corrects the gap. That correction lands as one large bill which looks exactly like a leak but is really ordinary usage catching up.
Rule out the ordinary explanations
- Someone extra in the house. A visitor staying, school holidays, a helper who has just started, a family member now working from home.
- A change in habits. More laundry, a new washing machine, longer showers through a hot stretch.
- A new fitting. A rain shower head moves far more water than the head it replaced, for the same length of shower.
- Recent plumbing or renovation work. Lines get flushed and tested, and that water is metered.
- The billing period itself. A longer period covers more days.
What a leak-shaped increase looks like
An explainable jump is usually a spike. One high period, then back to normal. A leak is a step. The bill goes up and stays up, and it tends to keep climbing, because the leak runs while you sleep, while you are at work and while you are away for the weekend.
If you have two or three periods in a row that are all high, stop looking for a change in behaviour.
Run the meter test properly
Our post on the signs of a hidden water leak covers the quick version. For a suspected slow leak, do it more carefully than a thirty-minute check.
- Turn off every tap. Do not flush a toilet, run a washing machine, or use an ice maker.
- Photograph the meter face, including the smallest digits. Photograph it rather than copying it down, because the last digits are the ones that matter and they are easy to misread.
- Leave it overnight, or for a full working day if the flat will be empty.
- Photograph it again from the same angle and compare.
A small movement over eight hours is still a leak. A large movement over eight hours is a leak to deal with now.
Many meters also carry a small spinning dial or a triangular indicator that responds to very low flow. If that is turning with everything shut off, water is moving somewhere.
Narrow it down to a fixture
If the meter moved, the next job is working out where. This is where most people stop and call, and it is also where twenty minutes of your own time saves a lot of hunting later.
Close the isolation valve on one fixture at a time and repeat a shorter meter test after each. The valves usually sit on the wall behind or below the fitting: under the sink, beside the toilet, at the heater. If the meter stops moving once you have isolated something, you have found it.
Start with the toilets. A cistern trickling silently into the bowl is the classic cause of a large invisible loss, because it makes no sound and leaves no puddle. Our post on why a toilet keeps running has the dye test that confirms it.
A fixture, or something in the wall?
The distinction matters, because one is a part and the other is a repair.
It points to a fixture if isolating that fixture stops the meter, if you can see or hear water moving in a cistern, or if the loss stops with that one valve closed and the rest of the flat still live.
It points to a concealed pipe if the meter keeps moving with every fixture isolated, if there is a damp patch, blistering paint or a soft skirting with no bathroom behind it, if a patch of floor is warm underfoot, or if you can hear a faint hiss with everything closed.
A concealed leak is not something to sit on. The water is going somewhere, and the bill is the cheap part of that damage.
When to call a plumber
Call once the meter has proved water is moving and isolating fixtures has not stopped it, or when you have found the fixture and it needs more than a washer. Our leak repair work covers tracing a concealed leak down to the smallest area we can before anything is opened up, and the pricing page shows what common jobs start at. Bring your two meter photos to the conversation. They save us a step, which saves you money.