leak under sink or condensation

smokeybear77

Hello,

I am looking to sell my house later in the year but would first like to get on top of a problem in a cupboard under my kitchen sink that has appeared in the last week. Every few days, some water (up to 50 mL) has been collecting (in a bowl) in this cupboard. It is also where the cold water mains pipe enters the house and it backs onto an external wall (west-facing). I would like to try and establish if it is arising from a leak or condensation. I don't want to lag the pipes or try to use insulating foam around the pipe entry point, if the root cause is a leak. This is what I know:

i) I am checking the area regularly (except for overnight). There is no regular drip. When the water appears, it does so suddenly or overnight.

ii) Its appearance does not seem to be linked to the use of the kitchen taps, nor the washing machine and dishwasher, which are on either side of the cupboard.

iii) Water does not seem to have leaked down when splashed around the sink surface (test for incorrectly sealed sink)

iv) The water still appeared when the cupboard door was left open and a dehumidifier operated next to it (as part of a test for humid air in kitchen condensing on water pipe), though not as much as without the use of the dehumidifier.

v) When the water collects in the bowl, there is no obvious condensation on the surrounding pipework, apart from a partly-formed drop on the U bend above the bowl.

IMG_20260217_170135375.jpg

vi) For the nights where the water has collected, the outside temperature has been close to 0 oC. (This may be a coincidence though.)

Are there any simple checks I can do to confidently rule out a slow leak?

MikeJXE

The bowl doesn't look as it's under the copper pipes so I'm thinking it has to be a leak in the plastic waste

WIAWSNB

Replace the bowl with a sheet of paper. Note where the drip lands. Trace straight up from there with a torch shining directly at each bit of pipe - look for the tell-tale sparkle.

Use kitchen paper applied flat on the pipes and under sink - damp should show up.

But, yes, almost certainly an actual leak, not cond. And very likely easy to sort.

glennevis

"Water does not seem to have leaked down when splashed around the sink surface (test for incorrectly sealed sink)"

Dry the U bend then put a couple of sheets of kitchen towel in the cupboard. Fill the sink past the overflow then pull the plug. You need to create a decent flow (and test the overflow for a leak in that pipe). My money is on the failure of one of the washers on the waste down pipes.

Easy enough to fix. Screwfix do a couple of good quality McAlpine kits of parts with the trap and pipes, depending on whether you have a double sink or single.

plumb1_2

there a iffy connection just below the half bowl