IPA: /ˈskʌm.ləs/
KK: /ˈskʌm.ləs/
Not having any layer of dirt or waste on the surface.
The water in the pond was scumless after the recent cleaning.
Scumless is formed from "scum" (from Old English *scuma*, meaning a layer of dirt or filth) and "-less" (meaning without). The word "scumless" means without scum or free from dirt and filth.
Think of being 'without' ('-less') any 'dirt or filth' ('scum') — that's what scumless means.