I recently noticed some white flaky stuff floating in the water coming from my kitchen sink. Google around indicates that it could be calcium carbonate but my understanding is that calcium carbonate sinks in water and this stuff floats on the top.

I have a water filtration system. It consists of three small filters under the sink. Not sure if maybe the substance is coming from there or what.

What is this stuff?

Update - 12/20/2021

I had someone from the city water come out and they had no idea what this stuff is. They said it's not calcium because it doesn't sink.

I did a little more thorough testing and found that it was indeed actually coming from the water filtration system I have under the sink. I don't know what that stuff is but I'm replacing the filter with another brand. And I'll be paying closer attention to the water from now on.

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  • Would check and/or replace the filters. A bit hard to tell white flakes from one to another without testing from a picture.
    – crip659
    Dec 15, 2021 at 22:11
  • Sea Monkey™ powder - it's extra protein!
    – FreeMan
    Dec 16, 2021 at 16:12

1 Answer 1


There are many possibilities. Making it more difficult to answer, small particles float on the surface tension of water, even as a dense steel needle can float. So it could be calcium carbonate, CaCO3, i.e., "lime". To test for that, stir in some vinegar or lemon juice to see if the particles slowly dissolve.

Another likely possibility is cellulose or glass fiber fragments from filtering material.

To be more definitive, you'd need to collect some material, examine it under a microscope (natural cellulose can be identified that way) and perform some more chemical tests.

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