I discovered this when doing a post-assembly indoor test of a Luftdaten air quality sensor I built[0]. I kept it running for few hours and then looked at the data, and saw some ridiculously high levels of PM2.5 and PM5 in the evening. I've decided to investigate it. Over the next two days, I figured out that the increased levels happen at times when our air humidifier is running, which led me to discover that those ultrasonic air humidifiers essentially atomize everything that was mixed with/dissolved in the water - and we were using filtered tap water with ours. With distilled water in the humidifier, the sensor did not show increased particulate levels.
We've mostly stopped using the humidifier now, because I can't find a source of distilled water that doesn't involve buying plastic bottles.
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.
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).
We've mostly stopped using the humidifier now, because I can't find a source of distilled water that doesn't involve buying plastic bottles.
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[0] - https://luftdaten.info/en/home-en/