sediment, grounds, dregs, stagnant
澱 centers on the heavy residue that settles at the bottom of a liquid: sediment, dregs, or grounds. The stagnant sense extends naturally from the idea of still, murky water where such sediment accumulates.
澱 combines 氵 (water) with 殿, which likely contributes the sound デン and carries a sense of settling or a base. The character expresses sediment settling in water.
Water 氵 beside a grand hall 殿: picture a stagnant pool in the courtyard of an old hall, with sediment and dregs slowly settling to the bottom.
For デン, imagine a den of stagnant water under the hall: den -> デン, and the murky den is full of sediment.