I've been saying this to people for a long time. Here in my country, most water filters are based on charcoal and a final filtering element. That element used to be made of cellulose and other organic materials, but in the last decade, they started coming with that element made of polypropylene, until all the cellulose ones disappeared from the market. Just imagine your water passing though a porous layer of plastic, like a rigid sponge... this is a serious microplastic source.