To check your water meter for a leak, read it last thing at night, use no water, and read it again first thing. If the number has moved, water is escaping. Divide the litres lost by the hours between readings to get a rate. Repeat with the internal stop tap closed to learn whether the leak is inside the house or on the buried supply pipe.
You suspect a leak. Maybe the bill jumped, maybe there is a damp patch nobody can explain, maybe South West Water have written to say your usage looks odd. Before you ring a plumber, an insurer or us, there is one test that costs nothing, takes two minutes of effort at each end, and turns a suspicion into a fact with a number attached. Do it tonight. When you do call, you will be able to say “the meter moved 60 litres overnight with everything off, and it kept moving with the stop tap closed”, and that sentence alone saves an hour of the survey. If the result says hidden pipe, our water leak detection service takes it from there.
Find the meter and learn to read it
In most Cornish homes the meter is outside, in a boundary box under a small round or square lid set into the pavement, the verge or the drive near the gate. In older cottages and many flats it is indoors, close to the stop tap. Farms and rural properties often have theirs at the roadside a long way from the house. Take a torch, a cloth and something to prise the lid up. The face of the meter shows:
- Black digits. Whole cubic metres. One cubic metre is 1,000 litres, and this is the figure your bill is calculated from.
- Red digits or small dials. Fractions of a cubic metre. On most meters the first red digit is 100 litres, the next 10 litres, the next single litres. A leak shows here long before it troubles the black numbers.
- A flow indicator. A small wheel, star or triangle on a mechanical meter, or a droplet or arrow icon on a digital one. It turns whenever water passes, however slowly.
If the box is full of water, bail it out first so you can read the face. A wet meter box does not by itself mean a leak, but if it keeps refilling in dry weather it is one of the clues.
The overnight test, step by step
- Get the house quiet. Every tap off, no dishwasher or washing machine cycles pending, no timed garden irrigation, and nobody flushing at 3am if you can manage it. If you have a combi boiler, it does not use mains water while idle. If you have a cold water tank in the loft, the ball valve will top it up after the last use, so allow it half an hour to settle.
- Read the meter and write everything down. All the digits, black and red, plus the time. A photo on your phone is ideal because it records both.
- Leave it at least eight hours. Overnight is easiest. A two-hour test will show a big leak but can miss a slow one, and a slow one is exactly the kind that runs up a bill for months.
- Read it again before anyone uses water. Same routine, all digits, time noted, photo taken.
- Compare. If every digit is identical, you have no leak on the metered supply. If any digit has changed, water passed through the meter while nothing was in use.
If you cannot manage a no-water night (a household with small children, a busy holiday let in August) do it during the day while everyone is out, or run two shorter tests on separate days and see if they agree.
The maths: turning two readings into litres per hour
This is the part people skip, and it is the part that makes the phone call useful. Take the second reading away from the first, in litres, then divide by the hours between them.
| Example | Reading at 11pm | Reading at 7am | Lost | Rate |
|---|---|---|---|---|
| Slow weep | 0412.632 | 0412.648 | 16 litres | 2 litres an hour |
| Running toilet | 0412.632 | 0412.760 | 128 litres | 16 litres an hour |
| Split supply pipe | 0412.632 | 0413.912 | 1,280 litres | 160 litres an hour |
Those readings are made up to show the sums, not real survey results, but the bands are typical. Multiply the hourly rate by 24 and then by 30 and you have a rough monthly volume, which is the number that explains the bill. Two litres an hour sounds trivial and is nearly 1,500 litres a month. Sixteen litres an hour is over 11,000 litres a month, and that is a metered charge you will notice.
The second test: inside or outside?
Once you know water is escaping, the next question is where, and the meter answers half of it. Close the internal stop tap (usually under the kitchen sink, sometimes in a downstairs toilet, garage or under the stairs in older houses) and read the meter again over another hour or two, or another night.
- The meter stops. The leak is inside the house, after the stop tap. Toilet cisterns, a dripping outside tap, a weeping compression joint under a bath, a pipe under a solid floor. Start with the toilets: drop a little food colouring in the cistern and see whether it appears in the pan without flushing.
- The meter keeps moving. The leak is on the supply pipe between the meter and the stop tap. In Cornwall that pipe is often old, often long, and often runs under a slate path, a granite wall footing or a tarmac drive. This is the case that most needs proper location before anyone digs, because responsibility for the pipe on your side of the meter sits with you, and so does the cost of a trench in the wrong place.
- The meter did not move on the first test either, but the bill is high. The problem may not be a leak at all. Estimated readings, a meter changeover or a tariff change can all do it. Read why a water bill suddenly doubles before going further.
Old stop taps in Cornish cottages sometimes will not close fully. If you turn it off and the kitchen tap still trickles, the stop tap is passing and the inside-or-outside result cannot be trusted. Note that down too; it is useful for us to know before we arrive.
What the result rules in and out
The meter only measures water on the mains supply. That matters, because several common problems are invisible to it.
- Central heating leaks. A sealed heating system is filled once and then closed off, so a leak on a radiator pipe under the floor does not turn the meter. The symptom there is falling boiler pressure, and the guide to why a boiler keeps losing pressure covers it.
- Waste and drain leaks. Water leaving a bath, shower tray or soil pipe has already been through the meter, so a wet ceiling under the bathroom with a still meter points at the waste side, not the supply.
- Rain and ground water. Penetrating damp through a cob wall or a raised ground level outside is not metered either. A still meter and a persistent damp patch is a strong hint that the water is coming from outside the plumbing.
So a clean overnight test is a genuinely useful result. It does not mean “nothing is wrong”; it means the mains supply is not the source, and the search moves on.
What to tell us when you ring
If the test shows a leak, these details make the survey faster and the report stronger, so have them to hand.
- Both readings, with times, and the litres per hour you worked out.
- Whether the meter stopped or kept moving with the internal stop tap closed.
- Where the meter is and where the stop tap is, and whether the stop tap closes fully.
- Roughly where the supply pipe runs if you know, and what the ground surface is (lawn, slate, concrete, tarmac).
- Any wet patches, warm patches, sounds of running water or greener strips of grass, and when they started.
- Whether you have been contacted by South West Water, because a leak allowance application will need the repair date and readings either side of it.
Armed with that, we arrive knowing whether to start with acoustic listening on the supply pipe or thermal imaging inside, and the report you get at the end is the one your insurer expects for a trace and access claim. We carry out leak detection across Cornwall, and an overnight reading from a customer in Truro or a farmhouse on the Lizard tells us as much as the first hour on site would.
Frequently asked questions
How long should I leave the meter test?
At least two hours, and overnight is better. A large leak shows in minutes on the flow indicator, but a slow weep of a litre or two an hour may not move a visible digit in a short test. Eight hours with no water used gives a result you can rely on and a rate you can quote.
Does the water meter test show a central heating leak?
No. A sealed heating system does not draw mains water while it is running, so a leak on the heating pipework will not move the meter. The clue for heating leaks is boiler pressure that keeps dropping and needs topping up. That is a separate check and a separate kind of survey.
The flow indicator is turning but the digits have not changed. Is that a leak?
Yes, a small one. The indicator responds to any flow at all, while the last digit only changes after a whole litre has passed. Leave the test running longer and the digits will catch up. A slowly turning indicator with everything off is the classic sign of a weeping joint or a toilet valve.
My stop tap will not close properly. Can I still test?
You can still run the first overnight test, which proves whether there is a leak at all. The inside-or-outside test needs the stop tap to hold, so if water still runs from the kitchen tap with it closed, tell us and we will isolate the supply another way during the survey.
Can I do the test if I only have an estimated bill and no meter?
No, an unmetered property has nothing to read. You can still check for a leak by listening at the stop tap at night for a hiss, checking toilets with food colouring, and looking for damp or unusually green patches along the supply pipe route. A survey can confirm the rest.
Meter moved overnight?
Send us the two readings and we will tell you what they suggest and how we would find the leak. The survey ends with a written report your insurer can use for a trace and access claim.
