I've encountered the same issue (high plastic bottle waste along with high cost). Short of boiling your own water outdoors to avoid polluting the indoor air, it's challenging to find a source for bulk distilled water.
Rain is essentially distilled water (evaporation from terrestrial water bodies and then condensation in the atmosphere). It picks up some contaminants in the atmosphere and some dissolved gases when it condenses but it's going to be mostly free of minerals (i.e. not be hard). So collecting rain water is one source of bulk 'distilled water'.
Yes, and it will also release the impurities/minerals into the air, which is what we're trying to avoid by using distilled/boiled water.
I live in an area with very hard water (around 300ppm), and the evaporated minerals are very visible in the air (and it leaves a white residue on the surrounding area).
> I live in an area with very hard water (around 300ppm)
Tangential, but being curious how hard that was relative to mine led me to discover that Thames Water (i.e. only useful to anyone reading in London) has a pretty good page at [0] - a summary on the site itself but the PDF is really worth a look, lots of numbers. Maybe it's a regulatory requirement, but I wouldn't have expected it to be so easy to get so much information from them about my specific (it serves many districts in and around London with different sources and equipment) water supply.
It's actually quite common for water authorities to publish quite detailed analyses of the water they provide. Doing such analyses is a core competency of being a water authority and, since they are mostly publicly owned, then published for consumers, often at a fairly detailed level.
(E.g. Canada Pension Plan, Morgan Stanley, Hong Kong based investment trust)
As I said, it may be a regulatory (Ofwat) requirement, but it isn't just a public body doing right by its citizens.
Interesting anyway, not that much of it means anything to me. Though apparently if/when I try brewing beer again I should add some magnesium. (It even lists the range that's helpful as a yeast nutrient, and above which contributes unwanted taste.)
Yes, my humidifier actually has filters you can buy, but it's a bit cost prohibitive (around $20/filter and with the hardness of the water they only last about 3 weeks).
I just use filtered water from my fridge or from my Brita. Haven't noticed any nasty build up in the humidifier or any hazy production. The larger Honeywell I use in the master bedroom is the top fill which is designed as filter free.