The bottom section, where you put water, is all crusty with white mineral deposits, even though I use filtered water, not tap water. How can I scrape or dissolve those off? I can't really reach in there with steel wool, and dish brushes don't provide enough friction to be effective.

Does anyone have experience with this? Please don't advise anything that you (or someone you know) haven't tried and found effective.
This is not a "machine." View link to photo for clarification.