When you use tap water in a humidifier, it will inevitably accumulate water scale inside it. This is bad, especially if the water scale is able to contact the internal circuit board.




I discovered that there's something called a "demineralization water filter" that can reduce the water-scale in humidifiers by 90%. I found two of them so far that might work for you:

• Crystal Quest // Water Pitcher + Crystal Quest // Demineralizer Water Pitcher Cartridge

• Crystal Quest // Countertop Water Filter, Single Cartridge style + Crystal Quest // Demineralizing Filter Cartridge (choose filter size = 2-7/8" x 9-3/4")




(The theory behind this -- The filters are designed to remove calcium and magnesium from the water, which appears like white dust in humidifiers. These filters don't eliminate 100% of the water scale, but they do reduce it a lot. The amount of material removed by these filters is measured in TDS: total dissolved solids. There are even TDS meters if you want to get really fancy.)




High TDS generally means "harder water", while extremely low TDS generally means it's distilled.

https://en.wikipedia.org/wiki/Total_dissolved_solids

https://www.amazon.com/ZeroWater-ZT-2-Electronic-Water-Tester/dp/B002UUTAI6