I've seen that on the kitchen wall, right where the water pipes go up to the floor above, there's a moisture stain that keeps getting bigger. I don't see any drips or anything, but the wall is all wet. Is there a leak inside the wall or is it condensation?
Have you already touched the pipe inside the wall or do you have access to it from the basement or attic? What nobody's mentioned is that if the leak is at a joint or connection, it can be soaking the wall without dripping visibly to the outside, especially if the pipe is embedded and the water gets absorbed by the surrounding material. Before calling a plumber, try shutting off the main water supply overnight and check if the stain keeps getting wetter or stops getting worse; if it stabilizes, it's almost certainly a leak inside the pipe itself, not condensation.
Is the stain growing quickly or is it more of a slow process? That'll give you important clues. If the wall is wet without visible droplets and the stain is getting worse, there's likely a leak inside the wall. Condensation typically leaves the surface damp but doesn't soak the wall like that, and besides you'd see it during times of temperature changes (when it's cold and the air is humid). A leak in a pipe, even a small one, soaks through the entire depth of the material and the stain grows because water keeps seeping through.
What you should do is touch the wall with your hand: if it's cold or extremely cold in that spot compared to the rest, it's probably condensation. But if it's warm or at normal temperature and the moisture persists or grows, it's almost certainly a leak. Also check if it smells moldy or if the paint is peeling; that means it's been wet for a while. Turn off the main water valve for a bit (an hour or so) and see if the stain stops growing; if it does, that confirms it's a leak.
I'd recommend calling a plumber to check it with specialized equipment. Waiting isn't an option because if the leak continues, the water damages the structure, promotes mold (which is a health problem) and your water bill is going to surprise you. They can often find the leak without needing to open up the whole wall - sometimes just by opening a small section where the stain is biggest.
Press the wall with your hand at different points and see if it feels warm or cold - that tells you almost everything. If it's warm, it's condensation (the hot water in the pipe cools down as it passes), but if it's cold and wet with no visible droplets, there's almost definitely a tiny leak inside. Something similar happened in my house a while back and it turned out a connection was loose inside the wall, so the moisture was spreading slowly without dripping out. If it's a real leak, the stain's going to keep spreading sideways and eventually the finishes will come off or mold stains will show up, so don't wait around. Call a technician who can use a thermal or moisture camera to confirm before you go breaking the wall for nothing.
If the wall is actually wet (not just damp) and the stain is growing, it's almost certainly a leak inside the pipe, not condensation. What nobody mentions is that slow leaks can be draining downward or sideways without you seeing it at that exact spot, so before you call a plumber, feel the walls below and to the sides too to figure out how far the moisture extends.
Log into answer.
