I am only a hobbyist in the darkroom so some things I do might make others cringe, but prior to using the filters I used only a 25Ám irrigation filter to take out the lichen and big grit. The results I got over 6 years were fine for my needs. No scratching or abrasion that I could tell.In saying that last June I used water straight from the Murray River to develop some rolls of film. I would not recommend it if your life depended on the resulting pictures, but I was happy with the results from the frames I could use.