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Question DetailsAsked on 3/18/2016

How can water flood under kitchen sink every few weeks when faucet / dishwasher have NOT been used for hours?

Every 2-3 weeks I enter the kitchen to find floor covered with water, coming from under the sink. It's getting more severe, going down the wall in back of the sink and flooding the basement floor. Shutting off cold water valve under kitchen sink stops it temporarily. My plumber is stumped. He fixed small leak under sink, but two weeks later the problem reappeared worse than ever. This time it seeped up around the kitchen faucet as well. I find it after several hours of NOT using the kitchen. I rarely use the dishwasher.

Everything was remodeled 7 years ago. Plumber advised replacing kitchen faucet, but he's not really sure that the faucet is the problem.

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1 Answer


OK - this should be EASY to solve, provided you get there soon after it leaks. Either follow through following logic, or skip to #10 and see if that sounds likely, seeing as how it has popped out above the faucet.

Using toilet tissue (shows water much better than other paper like paper towels), after you have wiped up the floor and bottom of the cabinet so you are not swimming, start at the highest point on the piping and cabinet walls and work down, wiping all around, till you hit wetness. Note each highest point (because with splashing and such there may be several), then look where you encountered water.

Now - possible causes and exclusions:

1) if you can use water and fill the sink and empty it without leakage, pretty much rules out leaking drain pipes

2) if not occurring during sink/dishwasher use, rules out the dishwasher drasin hose and the connection where the dishwasher drain hose comes into the piping or garbage disposal, also the air gap in the dishwasher discharge line

3) ditto to garbage disposal leaking - that would be most severe when it or sink on that side is in use

4) a mechanical type air inlet vent on the drain pipe letting water surges out - commonly looks like item G in this photo - if the air inlet valve sticks and there is a backup in the drain pipes, would leak out the top. Normally would be when emptying full sinki or using garbage disposal, BUT if you have a partial blockage in the drains pipe running the clothes washer for instance could cause enough of a backup to cause ti to leak if it is defective and not sealing right (which is a VERY common issue with Studor vents).

So - that pretty much rules out drains if you did not find a problem. Now - fresh water:

5) if you have an under-sink water purification unit or hot water unit, sometimes when they see a pressure surge in the pipes asw they operate they leak at the gasket on the unit, or at the threaded fittings to the piping

6) because it occurs as a one-time thing every few weeks, very highly unlikely to be a broken pipe or loose fitting - once they start leaking significantly they pretty much tend to keep leaking, at least somewhat

7) check out the dishwasher - the hot water pipe leading to it (probably flex copper tubing but might be reinforced plastic) and wipe the underside of the dishwasher. WARNING - to avoid contacting live connections unplug the dishwasher (almost always under sink) before wiping bottom of dishwasher, and use two thicknesses of paper towels instead of toilet tissue to avoid clumping up pieces under there and to protect against cuts. Note - there will be a lot of sharp metal edges on the frame underneath. If you can see in under clearly with a flashlight (after removing toekick plate) and it is dry under there, you can eliminate a leak at the dishwasher as a source without feeling around for water.

8) if does not happen when dishwasher is running, that rules out bad door or pump seals. There are a few higher-end brands out there that run a short cycle automatically every week or so to prevent water stagnation in the pump - so sometimes that can cause a leak if there is a bad seal, but should also happen when dishwasher is used to clean dishes.

This probably leaves two more possible, and if not solution by this point, most likely sources -

9) a mechanical surge suppressor air vent (as opposed to closed type) on the top of the plumbing, usually on back wall, which reduces water hammer. The best types are just a capped off stickup of pipe or a closed suppressor tube, but there are a type that lets air back in after a surge, and can stick open at times and let water spray out during a surge, which commonly occurs when washer valves open and close, and sometimes with shower or toilet use. Think back on when this has happened - unlikely to remember toilet use, but was shower/tub or washing machine in use just before it happened ?

10) a leaking faucet gasket, probably leaking only when there is a pressure surge in the lines. You say it seeped up around the faucet this time - unless your faucet is really loosly mounted or does not have a base gasket or caulking, more likely it came from the faucet and ran down from there. It may be that just a rebuild of the faucet (interior seals and moving parts kit replacement) is all that is needed.

Leaking of the two gaskets on the swivel spout on a single-handle kitchen faucet can leak around the bottom and/or top of the swiveling part, then may run down into the faucet base and out under the faucet into the cabinet, or may come out around the swivel collar and leak onto the surface of the sink rim and countertop, or even spray in severe cases like if the gasket has been cut. However, those gaskets usually only have pressure on them if the faucet is open, so water would be dribbling out of the faucet spout. Ditto if you have leaking valve seals or ball seals in a single-handle faucet - when they leak yuou get leakage at the spout or around the swivel housing constantly till fixed, not usually individual surges unless your house is seeing high pressure surges from the water supply line or water hammer from washing machine.


You said shutting off cold water under the sink solves it - if shutting off both hot and cold to the faucet solves it I would say #10 is likely, but I can't visualize (unless two-handle and running out under the bonnet right under the handle and then down into the cabinet from above) how just turning off the cold water would solve it. I guess you might have a crack or corrosion in the faucet on the cold side only.. With many models (unless pretty fancy) replacing the faucet is not a terribly expensive thing - commonly about $50-150 though if you go fancy you can get up into the $3000 range (YES, $3000 - and not even gold plated at that) - plus probably $75-150 labor charge for the fix.

I am not certain if shutting the cold water to the sink off "fixed it" unless you left the cold turned off for a month or so, considering it happens only every few weeks - but tht combined with the water seeping up around the faucet would tend to indicate, unless water was spraying vigorously all over under there, that the faucet or the connecting tubing to it may be the problem source.

Answered 4 years ago by LCD

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