Bacteria, Mold and Your Kitchen Sink

Why don’t kitchen sinks have overflow holes?

Sinks with overflow holes are not allowed in food preparation areas due to the possibility of providing a place for bacteria and mold to grow around the overflow—-stuff you might not want as a “food seasoning.”

Typical under mount sink

Typical under mount sink

In general, the area around sinks should be kept very well sealed and caulked in order for them to be more easily maintained and kept sanitary.  Wheather the sinks are self rimming sinks, or under-mount type sinks, the connection between the two should be properly caulked.  Of course the molded plastic type sinks where the sink actually becomes a seamless part of the counter top is by far the easiest type to maintain.

Under-mount sinks are very fashionable these days, for a nice “clean” look, yet they can actually be less sanitary than a self-rimming type unless one is very vigilant in cleaning the underside of the counter top where the sink is caulked to the bottom side.  Add to this—-in the case of granite—that the underside of the overhangs is usually “unfinished” and creates an ideal place for mold and bacteria to grow (kind of like the underside of the toilet tank where there is no enamel coating).

In the following picture you can see where the connection of the sink to the counter top has not been caulked, creating a gap where mold and bacteria WILL grow.

bacteria at sink connection

These sink/counter top connections make a good breeding ground for mold and bacteria


Except for cheese and miso soup, it is probably a good idea to keep most bacterias and fungal growths out of the kitchen all together.


Charles Buell, Real Estate Inspections in Seattle

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  1. Daniel Rogers says

    Is that a bacteria zap gun you have there?

  2. Sophia Katt says

    Don’t forget to make clear that the caulk should be specifically useable for high moisture environments. A lot of home enthusiasts use other types. Bad plan.

    • Charles Buell says

      Sophia, there are so many different caulks out there—some are of little use for anything and most have jobs they are better at. Always best to use the one made for the purpose it is to serve.

  3. Do you know anything about black mold and dry rot under neath kitchen sinks?? Also, do you know anything about sap like drippings near such black mold and dry rot??

  4. Hi,
    What do you do once there is mold growth underneath? we are 2 years post expensive remodel of our kitchen with granite undermounted sink. It does have mold around the caulking underneath despite me cleaning with heavy bleach , toothbrush. Nothing works to kill the mold. What can I do? thank you

    • Charles Buell says

      I would call a counter-top installation contractor familiar with this problem. They can “polish” the underside and re-caulk or they may have to grind the top so there is not so much overhang. You can also have the sink replaced with a top mount type sink.

  5. In the picture above — the closeup of that gap, one can see the major problem. That gap would mostly be eliminated if the cutout for the sink were larger, so that there is a very slight reveal of the actual top ridge of the sink. This is because the sink edge is actually slightly curved, and because this granite was cutout even smaller than the actual sink dimensions, you can clearly see that the sink rounds upward underneath the granite which makes that horrible gap. My installer leaves a very slight reveal of the top edge of the sink (like maybe an eighth of an inch. The result is a sink that fits absolutely flush and tight to the underside of the countertop.

    • Charles Buell says

      I agree Patrick—the inside of the cutout should be close to flush with the inside of the sink.

  6. Karly Mandell says

    So my sink looks almost identical to the second picture, including the mold and bacteria unfortunately, since it also was never caulked. Is there something that I can do to remedy it myself, without contacting an installation professional? Or does it need to be completely redone to get into the crevice enough to remove all the gunk?
    Thank you!

  7. We have a small amount of black mold around our kitchen sink, but I imagine there must be more underneath. Should we have a plumber pull out the sink to check. We are not ready to do a kitchen remodel but will be doing one sometime in the future.

    • Charles Buell says

      I cannot determine your comfort level around molds related to your sink. Typically in the location under the rim of the sink this area cam be cleaned normally and the likelihood of there being significant amounts hidden seem remote but there is no way for me to know your particular situation. Have a qualified plumber check out your installation to see if there are warranted concerns.

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