Damp Wall That Ignores the Rain? Check for a Hidden Pipe Leak

The patch on the wall has been there for weeks. It was damp in the monsoon, and it is still damp now that the rain has eased. Everyone assumes "seepage" and the first instinct is to call a waterproofing contractor. Sometimes that is right. But if the wall stays wet regardless of the weather, a pipe inside it may be the real culprit, and no amount of external waterproofing will dry it.

Rain seepage or pipe leak: the pattern tells you

Rain seepage follows the weather. It appears or worsens a day or two after rain and eases in a dry spell. A pipe leak follows your water use, or nothing at all. It stays damp in dry weather, and it may get worse when you run the washing machine, a geyser or a particular tap.

Signs the water is coming from inside the wall

• The patch is damp or darker in dry weather, including in the dry months.
• The wall is on the line of a bathroom, kitchen or utility wall, or a wall that shares a plumbing shaft.
• The damp patch is warm or feels different to the rest of the wall, which can point to a hot water line.
• Paint is bubbling or peeling, or plaster feels soft, even though the outside of the building looks sound.
• You can hear faint hissing or dripping near the wall when everything is quiet.
• The water bill has crept up without a change in how many people live in the house.

A simple check you can do today

1. Do the meter test. Switch off every tap and appliance that uses water, including the washing machine and any automatic fill. Note the reading on your water meter, wait an hour or two without using any water, and read it again. If a meter or flow indicator keeps moving, water is escaping somewhere on the supply side.
2. Check the usual suspects first. A running toilet cistern, a dripping tap or a leaking flexible hose under a basin can move the meter too. Look at our guide on under-sink cabinet leaks before assuming the worst.
3. Mark the patch. Draw a pencil line around the edge of the damp area and note the date. See whether it grows over a few days, and whether it grows when a specific tap or appliance is used.
4. Note which room is on the other side. Damp that lines up with a bathroom or kitchen wall suggests a line behind it. Our bathroom leak warning signs cover the related signs inside the bathroom itself.
5. Rule out damp from the ground. A tide mark low on a ground-floor wall points to ground moisture, not a pipe. See rising damp on ground-floor walls.

What not to do

• Do not paint or plaster over the patch. You will hide it for a few weeks while the wall and anything behind it keeps getting wet.
• Do not start breaking the wall at random. Narrow the location down first so you open up a small section, not half the room.
• Do not ignore it. A slow leak can damage plaster, paint, wooden fittings and, over time, the wall itself.

Who to call, and in what order

If the meter keeps moving or the damp ignores the weather, a plumber should isolate and test the line first. If the meter is steady and the patch gets worse after rain, you are back to seepage and waterproofing, covered in our seepage fixing guide. If you cannot tell which it is, that is where an inspection helps.

Where LoklFix fits

We find where the water is coming from before we suggest any work. If the evidence points to a pipe, we will say so and tell you to get the line tested first. If it is seepage through the wall, a window gap or the terrace, we fix that. No point treating a wall that a pipe is still soaking.

Frequently asked questions