Meter not moving but still losing water

The short answer

A still meter is evidence, but it is narrower evidence than it looks. It establishes that nothing large is running. It says nothing about a small continuous loss.

The reason is mechanical. A meter measures flow by being turned by it, and below a certain flow there is not enough force to turn it. That threshold is the starting flow rate, and on the Itron Aquadis+ DN15 R160, a volumetric rotary piston meter of the type widely fitted on UK domestic supplies, the manufacturer gives it as 0.4 litres per hour. Below that the meter reads the same before and after, however long you wait.

That is a small volume by household standards, which is the honest conclusion here: a leak the meter cannot see is a leak that is probably not costing much. What it may still be doing is soaking into something.

How this works in practice

The confusion comes from treating a meter as an instrument that is either accurate or inaccurate, when it actually has three separate regions of behaviour.

The two accuracy figures come from OIML R 49-1:2013 clause 4.2.3 for accuracy class 2, the domestic norm, and the in-service doubling from its Annex C, which is informative rather than mandatory. The flow rates come from the meter datasheet. The point of setting them out together is that the region most household leaks fall into, between the starting flow and Q1, is the region the standard says nothing about at all.

So the sequence of questions to ask about a still meter is not "is the meter accurate" but "is the loss large enough for the meter to be involved at all".

• Nothing registered over several hours with everything closed: any loss is below the starting flow, or there is no loss.
• A movement too small to read confidently: extend the test rather than round it. The rate is the volume divided by the hours, so a longer test shrinks the effect of a reading error.
• A clear movement: you have a rate, and take two readings over a measured interval converts it into volume and cost.

What changes the answer

Four things move the threshold, and two of them move it in the direction people do not expect.

• Connection size. The figures above are for a 15 mm meter, the standard UK domestic size. On a 20 mm meter the same manufacturer gives a typical starting flow of 2 litres per hour, five times higher, so a larger connection hides a larger loss. That figure carries no register footnote on the sheet, unlike the 15 mm one, so it is a typical value rather than a best case.
• Meter age and wear. Starting flow is a typical figure for a meter in good condition. A worn meter starts later, not earlier, so an old meter hides more than a new one rather than less.
• Meter type. Volumetric rotary piston meters, the type these figures describe, generally start at lower flows than jet meters. If your meter is a different type its datasheet will give a different figure, and that figure is the one that applies to you.
• Whether the loss is steady. A leak that only runs when mains pressure is high, or a toilet valve that passes intermittently, can average below the starting flow while exceeding it for part of the day. A test run across a whole night catches that. A two hour test in the afternoon may not.

None of this makes a still meter useless. It makes it a floor rather than a verdict: it tells you the loss is smaller than the meter can see, which is itself a number.

Assumptions and sources

Two of these figures need their status stating precisely. The accuracy tolerances are from OIML R 49-1:2013, an international recommendation that underlies UK domestic meter approval, and they are mandatory for the flow regions they cover. The starting flow of 0.4 litres per hour is not from any standard. It is a typical value published by one manufacturer for one meter, and the standard does not regulate it at all. It also carries a footnote on that manufacturer's own sheet: it applies to meters fitted with one particular register, and meters with a different register start higher. So it is the best case rather than the usual one, and the range a still meter can hide is wider than this page would suggest if the footnote were ignored.

That distinction matters more than it looks. It means the figure is a good indication of what a UK domestic meter does and a poor basis for a precise claim about your meter. Where the answer matters to you, the meter model is printed on its face and its specification is worth looking up by that model number.

The direction of the footnote is worth stating plainly, because it runs in the reader's favour rather than ours. If the quoted figure is the best case and other registers start higher, then the argument this page makes does not rest on the exact number. A still meter rules out less than 0.4 litres an hour would suggest, not more.

And the accuracy picture has a floor below the one the standard sets. The same manufacturer sheet states an error of ±5 per cent at 3 litres per hour and ±2 per cent at 5, and says nothing at all below 3. So a reading of 0.5 litres per hour sits six times below the lowest flow anybody has published an error for, from the standard or from the maker. That is not a meter behaving badly. It is a region neither document describes.

Volumes are converted using the definition of the cubic metre as one thousand litres, and years as 365 days.

What to do next

A still meter with a real suspicion behind it is worth testing differently rather than testing again the same way.

• Run the test overnight, or across a full 24 hours, rather than for two. An intermittent loss that averages below the starting flow will still move the meter during the part of the day it is running.
• Read the meter at the start and end of a billing period and compare the volume with the same period last year. A loss too small to see over one night is visible over three months.
• Look for the loss instead of measuring it. Water that never reaches the meter threshold still has to go somewhere: a damp patch that never dries, a warm spot on a floor, a manhole that runs when nothing is running, a section of garden that stays green.
• Dye-test the toilets. A slow pass through a flush valve is the most common small internal loss, it is silent, and it can sit under the starting flow for months.

If you have ruled out everything you can reach and still believe water is going somewhere, what to do when the meter cannot settle it sets out which losses a meter reading cannot localise, and what each detection method can and cannot find.

Common questions