What refills on its own and gets missed?

A water softener regenerating, an ice maker, a dishwasher or washing machine on a delayed start, a toilet still refilling after a flush, a heating system on an automatic filling device, and an outside tap left cracked open. All of them draw water without anyone being in the room.

How do I tell a leak from something refilling?

By its shape over time. Something refilling draws hard for a few minutes and then stops, so a series of short readings shows a burst and then nothing. A leak is steady: the same volume in every equal interval. Take three readings 30 minutes apart rather than two readings two hours apart, and the difference is usually obvious.

The meter still moves with the internal stop tap closed. What does that mean?

That the loss is between the meter and the stop tap, which on most properties means the underground supply pipe. That is a different problem from an internal leak: it is usually the property owner's responsibility to repair, it does not show as damp inside, and the water never reaches the sewer, so no sewerage charge should be applied to it.

Could the meter itself be faulty?

It is possible and it is uncommon, and it is not the first thing to suspect. A meter that over-reads is rare, and the check for it is the same test done properly: with the stop tap closed and nothing at all connected, a correctly working meter does not move. If it does, that is worth reporting to your supplier, because the meter is theirs.

Meter moving with everything off

A water meter that keeps moving with every outlet closed is measuring water leaving the system, and the movement is real. What it is not, yet, is proof of a leak. The most common cause is something in the property that refills on its own, and separating that from a genuine leak takes one more step: close the internal stop tap and read the meter again.

Last reviewed 14 August 2026

The short answer

The movement is real, and "everything off" is harder than it sounds. Before treating it as a leak, rule out the things that draw water without anybody touching a tap.

A water softener regenerating, which is designed to run when nobody is using water.
An ice maker in a fridge freezer.
A dishwasher or washing machine on a delayed start.
A toilet still refilling after a flush, or one whose fill valve is passing slowly.
A heating system fitted with an automatic filling device, which tops itself up as pressure falls.
An outside tap, or an irrigation timer, left cracked open.

None of those is a leak, and all of them put water through the meter. That is why the next step is a stop tap test rather than a conclusion.

How this works in practice

Two tests separate the three possible answers, and they take about an hour between them.

Take three readings thirty minutes apart with everything closed. A loss that is steady puts roughly the same volume through in each interval. Something refilling puts a burst through one interval and almost nothing through the others.
Close the internal stop tap, usually under the kitchen sink or where the supply enters the building, and take two more readings thirty minutes apart.
Compare. If the meter stopped, the loss is inside the building, downstream of the stop tap. If it did not, the loss is between the meter and the stop tap, which is the underground supply pipe.

That second result is the useful one, because it splits the problem in two before anybody starts looking. An internal loss is somewhere you can reach and is often findable with a dye tablet and a torch. A supply pipe loss is underground, will not show as damp indoors, and no amount of checking taps will find it.

Whichever it turns out to be, the size still has to be measured. the threshold a moving meter has to clear gives the figures a movement is judged against.

What changes the answer

Three things, and the last one is the reason this test can mislead in the other direction.

Whether the property is genuinely isolated. Every automatic draw above has to be off, not merely idle. A softener that regenerates at two in the morning is off at eight in the evening and will not show in an evening test.
Where the stop tap is, and whether it fully closes. An old gate valve can appear closed and still pass water, which reads as a supply pipe loss when the loss is actually inside.
The size of the loss. A meter that does not move does not prove there is no leak, because a domestic meter does not register below about 0.4 litres per hour. why a still meter does not rule a leak out sets out what an unmoving register does and does not establish.

Assumptions and sources

Aquadis+ DN15 and DN20 specification sheet

Itron · manufacturer source

Q1 minimum flow rate, DN15, Q3 2.5, R160: 15.6 l/h
Q2 transitional flow rate, DN15, Q3 2.5, R160: 25 l/h
Q3 permanent flow rate, DN15: 2500 l/h
Typical starting flow rate, DN15: 0.4 l/h
Typical starting flow rate, DN20: 2 l/h
Q1 minimum flow rate, DN20, Q3 4.0, R160: 25 l/h
Flow rate at which accuracy is within +/- 5%, DN15: 3 l/h
Flow rate at which accuracy is within +/- 2%, DN15: 5 l/h
Minimum scale interval, DN15 and DN20: 0.02 l

Where the first severity band ends

Editorial convention

A practical threshold set just above the 0.4 litres per hour starting flow quoted for a DN15 meter with the TVM register. It is not a meter accuracy tolerance. Against the STANDARD it sits about 31 times below Q1, the 15.6 litres per hour at which OIML R 49-1 first defines any permitted error. Against THIS MANUFACTURER it sits about 6 times below 3 litres per hour, the lowest flow at which Itron volunteers a typical accuracy that the standard does not require. Neither figure reaches down to 0.5, so nothing quantifies a reading here on either footing. Meters with other registers start higher, so this threshold sits above the most sensitive case rather than above every meter.

The diagnostic steps on this page are mechanical rather than measured: closing the stop tap splits the pipework at a known point, and comparing intervals distinguishes a steady flow from an intermittent one. Neither depends on a constant, so neither carries a citation.

The list of automatic draws is what is common in UK properties rather than an exhaustive or surveyed set. If something in your property refills on its own and is not listed, it belongs on the list rather than outside it.

What to do next

The stop tap result decides which of two different problems you have.

Meter stopped when the stop tap closed: the loss is inside. Dye-test every toilet first, because a passing flush valve is silent and is the most common internal loss. Then check taps, the loft tank if there is one, and any visible joint.
Meter kept moving: the loss is on the supply pipe. Look for ground that stays wet or unusually green, a chamber that refills, or a section of drive that dries more slowly than the rest.
Either way, measure the rate over a full night before deciding anything, and photograph both readings with their times.
Tell your supplier once you have a measured rate. The reading and the dates are the evidence a leak allowance is assessed on, and a supply pipe loss is the case the reasoning behind those allowances addresses, because it is a leak you could not have seen.

Common questions

What refills on its own and gets missed?: A water softener regenerating, an ice maker, a dishwasher or washing machine on a delayed start, a toilet still refilling after a flush, a heating system on an automatic filling device, and an outside tap left cracked open. All of them draw water without anyone being in the room.
How do I tell a leak from something refilling?: By its shape over time. Something refilling draws hard for a few minutes and then stops, so a series of short readings shows a burst and then nothing. A leak is steady: the same volume in every equal interval. Take three readings 30 minutes apart rather than two readings two hours apart, and the difference is usually obvious.
The meter still moves with the internal stop tap closed. What does that mean?: That the loss is between the meter and the stop tap, which on most properties means the underground supply pipe. That is a different problem from an internal leak: it is usually the property owner's responsibility to repair, it does not show as damp inside, and the water never reaches the sewer, so no sewerage charge should be applied to it.
Could the meter itself be faulty?: It is possible and it is uncommon, and it is not the first thing to suspect. A meter that over-reads is rare, and the check for it is the same test done properly: with the stop tap closed and nothing at all connected, a correctly working meter does not move. If it does, that is worth reporting to your supplier, because the meter is theirs.