There is a stain on the wall and you do not know whether it comes from rain, from the air in the house or from a pipe. A plumbing leak is one of the causes you can check with a simple test, without breaking anything. This guide explains the signs that point to a pipe, how to do the water-meter test with every tap shut, what the test cannot catch, who to call and what home insurance says about leak detection.
Updated 4 November 2026. General information, not a substitute for an assessment by a technician (plumber or leak-detection firm).
The essentials
- With every use of water switched off, the water meter should not move. If it does, a leak is very likely (Belmonte municipality).
- If the meter does not move, there is no active leak in the water supply at that moment. The stain may have another origin: drainage, heating, rain or condensation.
- The same council guide lists as indirect signs damp stains on walls, ceilings or floors, mould or smells, lower water pressure and an unexplained higher bill.
- Do not improvise: close the main stopcock if needed and call a qualified technician.
- Leak detection may be covered by insurance, but only in some policies and with a limit. Read yours before opening the wall.
Signs the stain may be a pipe
No single sign proves anything, but together they help you decide whether the test is worth doing.
- The stain does not depend on the weather. DECO PROteste (the Portuguese consumer body) describes a plumbing leak as a persistent stain, sometimes with mould, near pipes and sanitary fittings, unrelated to the weather. See the comparison with the other types in damp walls: the four types.
- It sits near a bathroom, kitchen, water heater or appliance. The Belmonte guide names cisterns, dripping taps, washing machine and dishwasher connections, water heaters and boilers, and visible pipes or valves showing corrosion or damp as critical points.
- Water pressure is lower, or the bill rose with no change in habits.
The meter test, step by step
The method comes from the guide “Suspeita de uma fuga de água em casa?” (“Suspect a water leak at home?”) by the municipality of Belmonte. It is simple and free.
- Switch off all uses. Turn off the washing machine, dishwasher and irrigation, and make sure every tap is fully closed. Nobody uses water during the test.
- Find the meter and note the reading, every visible digit. Take a photo, which serves as evidence later.
- Watch the flow indicator (needle or wheel). If it moves with everything off, a leak is very likely. If it is still, there is no active leak at that moment.
- For more rigour, run the longer test. Note the reading before a period with no water use (the guide gives overnight or a long absence as examples) and note it again at the end. If the reading went up, a leak in the building’s pipework is confirmed. If it stayed the same, there is no evidence of a leak.
What the test does not catch
The meter measures water coming into the house. So, and this is our own reasoning, not a statement from the sources:
- an intermittent leak may not show in a short reading, and the longer test helps;
- a sewage or rainwater pipe leak does not pass through the meter, because that water has already been used or came from the rain.
A still meter with a stain that keeps growing means the mains hot and cold supply is probably not the cause. It does not mean the wall itself is the cause.
If the meter moves: what to do
The Belmonte guide gives three measures: close the main supply valve if necessary, contact a qualified technician for a detailed inspection, and avoid improvised work that could make things worse.
Closing the isolation valve of each fitting one by one and seeing when the meter stops may give the technician a clue. It is a method from forum users, not from an official source.
Who to call
- A plumber to repair the pipe.
- A leak-detection firm when the pipe is buried in the wall and you cannot see where it fails. We found no reliable public prices for this service, so we give no figures.
- The water utility, if you think the leak is before the meter or the bill rose sharply. We could not confirm where the utility’s responsibility ends and yours begins: it depends on each utility’s regulations.
- The insurer, before breaking open any wall (see below).
Insurance: leak detection (“pesquisa de avarias”)
Finding the pipe that burst inside a wall costs money, and this is where insurance may help. What we read:
| Source | What it says |
|---|---|
| DECO PROteste | When a pipe bursts, the insurer pays the cost of locating the problem. Some policies also cover repairing the pipes, others sell that separately. Damage from slow seepage, damp and condensation, and from taps left open, is not covered. |
| Mapfre, Casa product (product information document, 23 June 2026) | The optional “Danos por Água” (water damage) cover includes leak detection up to 2,000 €. The excess depends on the age of the building or of the last full replacement of the pipework: none up to 20 years, 5% to 10% of the damage (minimum 150 € to 250 €) above that. Claims arising from lack of maintenance or poor insulation of the building are not covered. |
These figures are from one insurer and one date. Ask yours: do I have water damage cover? Does it include leak detection? What excess applies?
More on what home insurance covers and excludes is in home insurance: damp and leaks. Report the claim first and wait for the loss adjuster before opening walls.
After you find the leak
- Repair the pipe and only then deal with the wall. Painting over a wall that is still wet fixes nothing.
- Let it dry. We found no official drying time that holds for every wall.
- Only then paint, with the right preparation: see painting after a leak is fixed. If there is mould, the cause must be solved and the wall cleaned before any paint (see mould on walls).
If the water comes from the flat above, it is another conversation: see leak from upstairs: who pays. To work out how much paint you will need afterwards, use the calculator.
What we could not confirm
- What a leak search costs (thermography, tracer gas, ground microphone). We found no reliable public prices.
- An official waiting time between meter readings. The council guide says “a period with no use”, without minutes.
- Where the utility’s responsibility ends and yours begins. It depends on each utility’s regulations and we did not confirm it.
- That your policy covers leak detection. We only know what Mapfre says in the document read and what DECO PROteste says in general.
Sources (read on 4 November 2026)
- Municipality of Belmonte, Suspeita de uma fuga de água em casa?, PDF, May 2026: preparation, meter test, longer test, critical points, indirect signs and measures (read in full).
- DECO PROteste, Seguro multirriscos, como escolher?: leak detection, pipes and water-damage exclusions.
- Mapfre Seguros Gerais, Seguro Multirriscos Habitação, produto Casa, product information document, 23 June 2026: optional water damage cover, leak-detection limit, excesses and restrictions (read in full).
- DECO PROteste, description of a plumbing leak, cited through our guide damp walls: the four types, not re-read directly today.
- Portuguese news sites and forums consulted only for practical hints (15 to 30 minute waits, closing isolation valves), not used as a source of facts.