A sink that leaks only when it is filled up often has a problem with a seal that only gets wet when the water level is high, such as the overflow opening or the seal around the drain. A crack in the sink or water slipping past the rim or caulk can also be the cause.
This kind of leak can be confusing, because the sink may seem fine during everyday use. The water may only show up after you fill a basin to wash dishes, soak something or let a bathroom sink fill near the top.
Why the Water Level Matters
Some parts of a sink only come into contact with water when the basin is full or nearly full. If one of those parts has a weak seal or a crack, it may stay dry most of the time and then leak when the water rises.
That is different from a leak that happens only while water is draining, which more often points to the drain parts below the sink. Paying attention to exactly when the leak starts can help narrow down the cause.
Possible Sources of the Leak
Water that appears only with a full sink may come from:
- The overflow opening: many bathroom sinks and some kitchen sinks have a small hole near the top that drains extra water. The channel or seal behind it can leak when water reaches it.
- The drain seal: the seal where the drain meets the sink basin may hold up during quick use but seep when water sits on it for a while.
- A crack in the sink: a hairline crack high on the basin may only leak once the water level reaches it.
- The rim or caulk line: water splashing over or sitting along the edge can slip under failed caulk and drip into the cabinet.
These are possibilities, not a diagnosis. Water can also travel along the underside of a sink before it drips, so the wet spot may not be right below the source.
Safe Ways to Narrow It Down
Clear out the cabinet under the sink and dry everything well. Then use the sink normally and check underneath with a flashlight. Try not to fill it all the way to the top while you are watching for leaks, so a bad seal does not soak the cabinet.
Do not take apart the drain or loosen fittings to look inside. Old parts can crack or break, and that can turn a small leak into a bigger one. If water has damaged the cabinet floor, keep the area dry and avoid storing items there for now.
Repair Options
Many of these leaks can be fixed by resealing or replacing a gasket, drain part or caulk line. A cracked sink usually needs to be replaced. A plumber can check where the water is getting through and explain the options.
In Bronx apartments, report the leak to the super, since water in a sink cabinet can sometimes reach the floor or the unit below.
If your sink only leaks when it is full, we can provide help with a sink plumbing problem and find the seal or part that is letting water through. Call (929) 209-6183.
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