Hidden Leak detection

Question

How do I get a hidden leak detected? My smart meter shows a usage of 4 litres per hour even during the twilight hours. Thames Water is saying that it’s below the threshold for them to get involved

Marvin · Accepted Answer

The first thing I’d do is work out whether the loss is inside the house or on the underground supply pipe. Thames Water actually recommends a stop-valve test for suspected leaks.

1. Make sure absolutely everything is off — taps, toilets, washing machine, dishwasher, outside taps, boiler filling loop, etc.
2. Turn off your internal main stopcock where the water enters the property.
3. Leave it off for at least 30–60 minutes, preferably while watching the smart-meter data.
4. If the meter stops recording the 4 L/hour, the problem is somewhere after the internal stopcock, so I’d concentrate on toilets, concealed pipework, tanks, outside taps and appliances.
5. If it continues at roughly 4 L/hour with the internal stopcock closed, that’s a strong indication the leak is between the meter and your internal stopcock — usually the underground incoming supply pipe.

Darryl · Answer

Turn off internal cold main and check external meter. If still spinning you have a leak on the incoming main

Brian · Answer

Hi Hareesh — frustrating when your water usage is up but no one can see where it's going! Great that your smart meter is picking it up though — that's the first clue.

Here's what you can do:

🔹 Call a local leak detection specialist — they use acoustic listening devices, tracer gas, and thermal imaging to find leaks under floors or underground without digging everything up. Worth every penny when you don't want to tear your house apart!

🔹 What to expect: A survey usually costs £150–£300 depending on the property size. They'll pinpoint exactly where it is so you only dig where you need to.

🔹 Check your insurance: Some policies cover the detection cost — worth a quick call to them.

4 litres an hour doesn't sound much but it adds up — and finding it early saves far more damage and money later. Hope you get it sorted! 💪

Shane · Answer

Would need a plumber to investigate all pipe work, fittings, tapes etc and connection to locate damp spots where water is present

Gary · Answer

If its under ground outside then you cant really but if you chevmck no taps are dripping, check no tank overflows running outside, make there is no water trickling into any toilet pans, very common if syphon is letting water seep from cistern into pan, would mean new syphon or ball valve in xistern, check for any leaks on internal pipework that is vissible, look for wet patches on walls or ceilings.

Gary · Answer

I would have a local plumber come in check for signs of water in ceilings, walls and also to do a pressure check all round the property to see if you can locate it that way

Gavin · Answer

sounds to me could be your toilet best way to check if you have a faulty float valve is stick something flat on the back of the pan and watch carefully to see if water is running onto the object i tend to use a screwdriver flat head or a scrapper if not fro the toilet, dripping taps and if not that you will have to do a dye test through the property as you may have a pinhole in your pipe system.
if you want investigation works get in touch

Dan · Answer

There are several ways you can look into this, turn all your taps off, one by one, any Leaking Toilet toilets look into the Pan to see if there’s water trickling into it, if there is your isolate these individual items and see if the water stops once you’ve done this, the other, and more expensive way would be to debt a Leak detection agent in, but this is quite costly, my advice would be to try to find it yourself if you have an internal Stopcock turn it off, if the dial is still spinning in the street then you know that the water leak is outside from the Pipe Work from the external Stopcock to the internal Stopcock

Hidden Leak detection

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