How to read a water meter
A UK domestic water meter reads in cubic metres, and the digits are split. The black digits are whole cubic metres, which is what you are billed on. The red digits, or the ones after a decimal point, are fractions of a cubic metre. A leak test needs every digit written down, because a household loss shows in the red ones long before it moves a black one.
Last reviewed 14 August 2026
The short answer
Write down every digit on the register, in order, including any on a red background or after a decimal point, and note the time you did it.
| Part of the register | Unit | What it is for |
|---|---|---|
| Black digits | cubic metres | What your supplier bills. Moves slowly, so on its own it is useless for a leak test. |
| Red digits, or digits after a decimal point | fractions of a cubic metre, down to 1 litre on many meters | Where a household leak shows. This is the part the test depends on. |
| A separate small dial or pointer, where fitted | fractions of a litre | A leak indicator. Useful for seeing that something is moving, but read the digits for the number. |
Register layouts differ between manufacturers and between installation dates. Where the markings on your own meter disagree with anything here, the meter is right and this page is wrong.
How this works in practice
Four steps, and the third is the one people skip.
- Find the meter. It is usually in a covered chamber near the property boundary, and sometimes indoors near the internal stop tap.
- Clear the face. Lift the cover, and if there is a hinged plastic flap over the register, open it. Silt and condensation are normal.
- Write down every digit, left to right, including the red ones, and write the time next to it. A photograph on a phone is easier and it timestamps itself.
- Read it again after a measured interval, the same way, with the time.
The reason the third step matters is arithmetic. The rate is the volume divided by the hours, so a digit dropped from the reading does not make the answer slightly wrong, it makes it wrong by a factor of ten. take two readings over a measured interval does the division for you once you have both.
What changes the answer
Four things, and the first two decide whether the reading is about your property at all.
- A shared supply. If one meter serves more than one property, it measures all of them, and any movement you record may belong to a neighbour. Nothing on this page fixes that.
- Which side of the boundary the meter sits on. A boundary chamber meter measures the supply pipe as well as the property, so a loss on the underground pipe shows. An internal meter fitted after the stop tap does not measure that pipe at all, so an underground loss is invisible to it.
- Units. Some older meters read in imperial gallons rather than cubic metres. The test still works, because it measures a difference, but the conversion to cost needs cubic metres.
- A meter that is hard to see. Ground water in the chamber, a stiff cover, or a register facing away from you all tempt a guessed digit, and a guessed digit is worse than no reading.
Assumptions and sources
Litres in a cubic metre
Exact by definition
SI definition. The litre is defined as one cubic decimetre, so one cubic metre is exactly 1,000 litres.
Litres in an imperial gallon
Exact by definition
UK legal definition. The imperial gallon is defined as exactly 4.54609 litres in United Kingdom weights and measures law.
This page states what holds across UK domestic register designs rather than cataloguing them. Meters vary by company, by manufacturer and by installation date, and this site has manufacturer documentation for one widely fitted model rather than a survey of the fleet. Where a specific figure for your meter matters, its model is printed on its face and the manufacturer publishes its specification.
The one conversion used throughout is definitional: one cubic metre is 1,000 litres.
What to do next
With a reading and a time written down, the next step is the second reading.
- Close every outlet, leave the property unused for at least two hours, and read again. Overnight is steadier.
- Judge the movement against a threshold rather than against instinct. what an overnight movement of that size means gives the figures.
- Photograph the register at both readings. It removes any argument about what was written down, including with your supplier later.
Common questions
- Which digits do I actually need?
- All of them. One cubic metre is 1,000 litres, so the black digits alone change far too slowly to measure a leak. A loss of 5 litres per hour takes more than a week to move the last black digit and shows on the red digits within the hour.
- Where is my water meter?
- Usually in a small covered chamber in the pavement or driveway near the boundary of the property, and sometimes inside near the internal stop tap, commonly under the kitchen sink. Which one you have depends on when and by whom the supply was fitted rather than on anything you can change.
- The meter is under water in its chamber. Can I still read it?
- Often yes. Ground water collects in boundary chambers routinely and it does not mean anything is leaking. The face is usually readable through it once any silt has settled, and a torch held at an angle helps. If the chamber refills as fast as it is emptied, that is worth reporting to your supplier, because the chamber sits on their side of the boundary.
- What if my meter reads in gallons rather than cubic metres?
- Some older meters read in imperial gallons. The test works exactly the same way, because it measures a difference between two readings rather than an absolute volume, but the conversion to cost needs the volume in cubic metres first.
- Is a smart meter read any differently?
- The register reads the same way, in cubic metres, and the same digits mean the same things. What a smart meter adds is that the reading is taken automatically and often, so a small steady loss is easier to see in a run of readings than in two taken by hand.