Under my sink there is a leak somewhere which is causing the concrete floor under the sink to be soaked and it's seeping under the slate floor too. I can't seem to work out where it's coming from. I know it's hard to know without physically looking, but wondered if anyone had any ideas or pointers.

All of the pipes seem dry and seems to only happen when either the washing machine has been on or after washing up a lot. I opened up the waste to ensure the pipe is clear and it is. I'm wondering if it's the mains water in but below the surface. Below is a picture of under the sink.

Any help would be greatly appreciated!

under the sink

Blue - in/out to dishwasher (not in use)

Green - water to washing machine

Orange - washing machine waste

Yellow - mains water into house

Red - waste pipe going into the floor for sink, washing machine and dishwasher

  • 1
    Holy cow call Rube Goldberg someone stole his plumbing plans. Below the red dot appears to have leakage residue , residue can point to a leak. – Ed Beal May 16 '20 at 17:39
  • Shouldn't the washing machine waste connection be before the trap? As is, sewer gases can enter the washing machine. – Steve Wellens Jun 16 '20 at 13:36
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    Asking us for statistics isn't really going to help you. Look at the evidence. Run some water and find what's wet. Snug up all the compression fitting nuts that aren't fully hand-tight. – isherwood Jun 16 '20 at 13:50

Check the seal around the faucet, around the sink, and between sink and backsplash by having someone pour water there while you look below.

Failing that, wrap toilet paper around all the pipes. Wait. Check for a wet spot on the toilet paper. Here's your leak. This works better with colored toilet paper (pink, blue, whatever) as it becomes darker when wet.


Also, dont forget leaking past the edge of the sink - took me ages to find once as it dribbled down the nearest pipe which I accused of leaking.

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