the unit I have has no storage tank. The water comes out a tube that needs to fill something. We have a regular daily pitcher that gets filled several times through the day. I also fill up larger storage emergency water camping tanks. I guess those are made out of some kind of plastic.

I heard some RO filters could pass microplastics. I think it would be cool to see if any of that pics up in a microscope. What size particles are people zeroing in on exactly?