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Sorry for the possibly wrong terminology. I'm not a chemist and I'm not a native English speaker.
Please edit the question as needed. Thank you.

Is it possible to buy or prepare a dispersion with the following properties?

  • the particles should be >0.1μm in size, for example 0.11μm - 0.2μm
  • there must be a way to detect them - even in a small amount (colour, taste, chemical reaction with something else, ...)
  • it mustn't be a "glue"; it must be possible to flush them completely away with water or something else readily available
  • it mustn't be a toxic or corrosive substance
  • the dispersion (or components to prepare it) should be readily available (drugstore, grocery etc.)
  • the total price shouldn't be higher than $20 (I know this difficult with prices different in every country - this is just a guideline)

Why do I need it?
There's a very slight chance that a Sawyer Micro Squeeze Water Filter might have been exposed to a below zero temperature and might have been damaged by frozen residual water.
The manufacturer says there's no way to test the filter functionality in that case and a new filter should be bought instead. I wonder if this is really needed or there's a way to test the filter at home.

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  • $\begingroup$ Thanks for the answer & all confirming upvotes. As stated above, I'm not a chemist and don't know how to reword the question to be acceptable for this SE site. Is it possible to move it to outdoors.stackexchange.com with the last paragraph only and the accepted answer? (This is probably the right SE site for this question.) $\endgroup$ – user681768917 Sep 27 at 17:28
  • $\begingroup$ I think this question was ok, perhaps added additional tags would be good, but otherwise it's prompted a really good answer that addresses a common problem which non-chemists would otherwise not have thought a good solution to. $\endgroup$ – Buck Thorn Sep 27 at 17:46
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Try to get some clay and shake it vigorously with water. Let it settle for a several hours. Test your filter with the supernatant water and collect the filtrate in a very clean glass tumbler. Colloids have an interesting property of scattering light. In a dark room, try to shine light (ordinary flashlight might work or perhaps an ordinary pointer used in presentations/offices). Be careful, never ever look at the pointer directly. Look at the filtrate at $90^o$ (right angles to the light beam), if you see a light beam travelling in water, it means that colloidal particles are seeping through the filtrate and the filter is damaged.

Read more about the Tyndall Effect https://www.sciencesource.com/archive/Tyndall-Effect-SS2423500.html or on Wikipedia before doing anything.

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