The clearest sign of a hidden water leak is a water meter that keeps moving when every tap, appliance and toilet in the house is off. Other strong signs are a boiler that keeps losing pressure, a patch of floor that feels warm underfoot, damp or staining that grows, the sound of running water when nothing is running, and a mains supply that has become noticeably weaker.
You can test for most of these yourself in a few minutes. Doing so tells you whether the leak is on the mains cold supply or on the heating system, which are separate circuits and are traced in different ways.
The meter test
If you have a water meter, turn off everything that uses water, including washing machines and outside taps, and make sure no toilet cistern is refilling. Note the reading, or watch the small dial that spins with low flow. If it moves over the next half hour or so, water is going somewhere. Many Scottish homes are not metered, in which case the listening and pressure checks below matter more.
Next, close the internal stop tap. If the meter stops, the leak is inside the house. If it keeps turning, the leak is probably on the supply pipe between the boundary and the stop tap, which is often under a path, drive or garden.
Heating system signs
A sealed heating system is a closed loop and should hold its pressure. If the boiler gauge keeps dropping and you keep topping it up, water is leaving that loop. Before assuming a buried pipe, check the obvious places: radiator valves, the pipes under the boiler and the small copper pipe outside that runs from the pressure relief valve. A relief valve dripping outside is a common cause and a much simpler fix.
Warm spots on a solid floor, particularly over a heating pipe route or in a room with underfloor heating, point to a leak in heated pipework.
Signs around the house
- Staining on ceilings below bathrooms that returns after drying out
- Skirting boards swelling, flooring lifting or grout darkening in one area
- A musty smell in one cupboard or room with no obvious cause
- Hissing or trickling in walls or under floors at quiet times
- Mould appearing in a spot that is not normally damp
- Weaker flow at taps than you are used to, with no change from your supplier
Things that look like leaks but are not
Condensation is the usual impostor. Cold external walls, bathrooms without adequate extraction and windows streaming in winter all produce damp that is not coming from a pipe. Condensation tends to appear on the coldest surfaces and gets worse after cooking, bathing or drying clothes indoors. A leak tends to be in one place and gets worse regardless of the weather. Our bathroom ventilation guide covers the difference in more detail.
What to do next
If the leak is slow and you cannot see it, a leak detection survey is the right next step, because it finds the fault without opening up large areas on a guess. If water is visible, coming through a ceiling or you cannot stop it, close the stop tap and treat it as an emergency. Keep notes of the pressure readings, meter readings and photos; they speed up whoever attends.
Frequently asked questions
- How do I know if the leak is on the mains or the heating?
- If your meter moves with everything off, the mains is involved. If the boiler pressure keeps dropping but the meter is still, the heating loop is losing water.
- Can a hidden leak cause a high water bill?
- On a metered supply, yes, because you pay for water that runs to waste. Most Scottish homes pay water charges with council tax rather than by meter, so there the damage is the bigger concern.
- Is a dripping pipe outside the boiler a leak?
- It is usually the pressure relief valve discharging, which means the system pressure is too high or the valve is faulty. It needs looking at but it is not a buried leak.
- Should I keep topping up my boiler pressure?
- Topping up occasionally is normal. Needing to do it every few days means water is escaping and should be traced, because fresh water brings in oxygen that corrodes the system.
- Who is responsible for the supply pipe?
- Generally the pipe within your property boundary is the owner's responsibility, while Scottish Water looks after its own pipework up to the boundary. Check with Scottish Water if you are unsure where the line falls.
Found one of these signs?
Tell us what the meter or boiler gauge is doing and we will advise on the next step.