I learned to avoid tap water due to mineral powder ruining carbon filters and generally creating a mess. Distilled cured the problem but can eat into the pockets over time. RO would work also if that's an option. Fortunately for me I'm able to harvest rainwater. When it gets down to 10 ppm or less I collect. Gubment website gives treatment guidelines for collected water. In my case I use 7-8 drops of bleach/gal for storage. Powder residue problem eliminated and noticed also cleaning of humidifiers not eliminated but greatly reduced whether using distilled or rain water. The slime that accumulates in the unit isn't mold IMHO but rather algae. Cleaning wouldn't be eliminated but reduced.