What Is the White Powder from Ultrasonic Humidifiers and Is It Harmful?

[russ_watters]

TL;DR Summary

What is the white powder a humidifier emits and is it harmful to breathe?

Ultrasonic humidifiers atomize water and inject it into the air, where it evaporates. Anything dissolved in the water precipitates out as a white powder, which is noticeable as dust on surfaces throughout the room, especially near the humidifier. If the output is high enough, it can even form a visible white cloud throughout the room. Obviously that means we breathe it. So the question is, what is it and is it harmful?

For additional context, I bought a PM2.5 detector (2.5 μm and larger particles) after the wildfires last summer. The results are interesting. (Maybe later we can discuss the hazards of gas cooking and microwave popcorn...). Among the results are poor air quality readings in my bedroom with my combination ultrasonic/evaporative humidifier on. This morning in a test it read 160 μg/m³, which is "unhealthy" According to the WHO. It reads in single digit precision and can read as low as 0-1 if the HVAC has been running a while or I'm using my air purifier. Now, of course not all particles are created equal, and this scale was invented to measure particulate air pollution, which is mainly a nasty carbon soot cocktail. But what about what this humidifier is putting out?

I've done some "research" and the results are thin. Sources mainly just say it's the same stuff as in drinking water, so that means it's fine. Be we all know that drinking and breathing it aren't the same. And it may not even be the same chemical in each case. Note, the EPA says research has not found a risk, but a medical case report claims injury to an infant due to sustained exposure.

My tap-water source is very hard (primarily calcium and magnesium), but I use a softener. I don't have any bags of the salt it uses, but google tells me it's sodium chloride - table salt. The softener uses an ion exchange process that removes calcium and magnesium and leaves the sodium. Does the sodium stay dissolved? Pure sodium metal explosively reacts with water to form sodium hydroxide (NaOH). Does this happen just after the ion exchange? These questions are why I put this in the chemistry forum.

An SDS I found for sodium hydroxide lists an inhalation hazard level of 1 mg/m³. An SDS for sodium metal mentions "metal fume fever" as an inhalation hazard, which doesn't sound good, but they don't list concentration guidelines.

Thoughts?

For now I'm running my hated air purifier when the humidifier is on.

 

[BillTre]

There can be lots of stuff in hard tap water.

You could be able to get a report from your water utility listing the chemicals in it. These reports however can vary in quality and will only show what's in there since the water left the water factory. If you live in Flint, MI for example lead might have been added after leaving the factory.
I suspect figuring out everything in there might be difficult.
If you collect the residue, you might be able to redissolve it and test it with specific consumer tests for specific chemicals like lead.

Its my understanding that particles breathed in could be physical irritants. If they dissolve, this may not be a problem. Does all the residue dissolve? I would expect this to happen when the contaminated air contacts mucus and other fluids.

The simplest solution might be to use a cleaner source of water. Probably depends on how much water you use.
I have a RO/DI system for my fish which would work well, but not everyone has this kind of thing and it takes room and a bit of an install.
Alternatively, maybe buy water jugs.

My wife loves her air purifier.

 

[Bystander]

TL;DR Summary: What is the white powder a humidifier emits and is it harmful to breathe?

My tap-water source is very hard (primarily calcium and magnesium), but I use a softener. I don't have any bags of the salt it uses, but google tells me it's sodium chloride - table salt. The softener uses an ion exchange process that removes calcium and magnesium and leaves the sodium. Does the sodium stay dissolved? Pure sodium metal explosively reacts with water to form sodium hydroxide (NaOH). Does this happen just after the ion exchange? These questions are why I put this in the chemistry forum.

Sodium sulfate N hydrate.

 

[.Scott]

When the calcium and magnesium are removed, they are removed in salt form. For example, as magnesium or calcium chloride. There is no metallic sodium in water solutions.

In the case of very small amounts of very soluble salts (such as common chlorides or nitrates), administering them in solution form through breathing or eating would be very similar. If there is any difference, it might be in the percentage of the material that makes it to the blood stream - and I'm not sure which would be more effective in that sense. But since the original dosages would not be the same, that comparison doesn't really matter. For example, if you have a heavy metal in your water (for example, lead oxide), your digestive system might be able to precipitate some portion of it out of solution - sparing it from your blood stream, quite a bit of it would still make it through. But you're likely to drink much more than you inhale.

 

[gmax137]

The simplest solution might be to use a cleaner source of water. Probably depends on how much water you us.

I ran my humidifier on distilled water (in gallon jugs from the grocery store). I still had the white powder residue. I got rid the humidifier, and live with the dry air.

 

[Borek]

Most of the salts in the white residue should be easily soluble (as it was already explained: softener just replaces Ca²⁺ and Mg²⁺ with equivalent amounts of Na⁺, sodium salts - as opposed to salts of calcium/magnesium - tend to be quite soluble, to the point they are difficult to detect in classical cation analysis based on salt precipitation).

At the same time: it is just a guess on my side, but some of the solids in the dust can be insoluble. Water can always contain some tiny amounts of silicates, they can easily decompose on drying - so in the end you can be breathing sand (SiO₂). In a very tiny quantities, and it is at worst an irritant, not a poison, but still.

 

[Borek]

I ran my humidifier on distilled water (in gallon jugs from the grocery store).

It is called "distilled", but as far as I am aware it is just deionized (either by methods similar to those used by the softener, or by reverse osmosis). Not exactly the same.

 

[JT Smith]

At the same time: it is just a guess on my side, but some of the solids in the dust can be insoluble. Water can always contain some tiny amounts of silicates, they can easily decompose on drying - so in the end you can be breathing sand (SiO₂). In a very tiny quantities, and it is at worst an irritant, not a poison, but still.

Maybe not a poison, per se, but at some point exposure can result in silicosis. Not likely a concern in this instance.

 

[Tom.G]

Just put a large-ish shallow pan of water near the outlet of whatever forced air circulator you have in the room, or use a fair size low speed (low noise) fan to move air over the pan.

With forced air central heating, there are humidifiers to install in the air ducts; rather high maintenance though.

Cheers,
Tom

 

[russ_watters]

Thanks all. A few responses to several of the noted items:

• I should be able to collect some powder or scale from the boiler section to see if it can be re-dissolved. I'm guessing no, and that's what I was concerned about. Chemistry-wise I wasn't sure if something could be dissolved, precipitate out, and then not be capable of re-dissolving.
• Water quality report, not comprehensive, just hits many of the troublesome contaminants (uranium? awesome). It doesn't list what's likely the main contaminant, the hardness, and I'm not sure that matters anyway because I'm using a softener. Though I suppose it could tell how much of the replacement chemicals there has to be. Anyway, I'd tested it before: 250 ppm/14.6 gpg.
• RO/distillation: I've looked into RO and I'm considering it. And I've tried store-bought distilled water and got the same surprise as @gmax137. It was a lot less dust, but not zero. I'll probably keep using it though, for now.
• Yeah, @BillTre my ex-girlfriend loved my air purifier too. Don't get me wrong, it works great, I just mostly hate the industry hyping/selling over-priced, poorly made and many poorly performing products. There's almost no way to avoid getting at least two of the three, so I picked the first two.

 

[russ_watters]

It is called "distilled", but as far as I am aware it is just deionized (either by methods similar to those used by the softener, or by reverse osmosis). Not exactly the same.

What is the difference, besides process, between distillation and RO (difference in output I mean)? I thought the point of either was to effectively remove/filter-out contaminants leaving you with pretty pure water. The Navy ship I was on used both RO and actual distillation to create potable water from seawater. I wouldn't care much about which process is used for the store-bought as long as the name referred to such a purification process. It sounds like very false advertising if it's just softened water. Heck, I've been using it in my iron for years for that reason.

....this would also imply that "purified water" in the store is closer to distilled water than "distilled water" is? Very confusing and maybe very false advertising. I guess my question is which if any should I be buying to not get scale? Maybe I'll need to do my own testing...

 

[russ_watters]

Just put a large-ish shallow pan of water near the outlet of whatever forced air circulator you have in the room, or use a fair size low speed (low noise) fan to move air over the pan.

It would surprise me greatly if that could create enough humidification to replace a humidifier, but I've never tested it. I've always assumed that was an old-wives tale.

With forced air central heating, there are humidifiers to install in the air ducts; rather high maintenance though.

Yeah, I'm considering that too.

 

[BillTre]

What is the difference, besides process, between distillation and RO (difference in output I mean)? I thought the point of either was to effectively remove/filter-out contaminants leaving you with pretty pure water. The Navy ship I was on used both RO and actual distillation to create potable water from seawater.

There are subtle differences that refined users of high quality water would be aware of.
People I know like that are:

• growers of fish and other aquatic things (some are very sensitive to particular chemicals)
• People doing chemistry in a lot of different kinds of labs (like molecular biology, physiology, cell/tissue culture, pharmaceuticals). Also some are very sensitive to particular chemicals.

Different kinds of chemicals can get through different purification processes.
I have had chlorine go through a still with the steam and end up in the distilled water.
Modern ion exchange columns will remove specific kinds of unwanted charged molecules.
Charcoal (carbon) is good at removing organics as well as other stuff.
RO membranes only let things below a certain size get through.

For high purity purposes a combination of these are often used.
There are tradeoffs between cost, purity, and volume (duh).
Volumes can be hundreds of gallons/day to a few mls.
Some fish farmers measure water in metric tons (cubic meter).

Most of these high levels of purity don't matter for human consumption (food grade, which is usually pretty good), but it can show up in other ways.

It seems to me that if you use completely clean water to begin the process, then the dusty material has to come from somewhere else such as:

• dirty machine, pipes, or container
• some weird chemical reaction with something in the air (???!!)

Personally I like your idea that its water hardness/water softener material.
Water softeners take out some ions (like Ca++) but put in others (Na+). Those (Na+) might be soluble.

Just put a large-ish shallow pan of water near the outlet of whatever forced air circulator you have in the room, or use a fair size low speed (low noise) fan to move air over the pan.

This has not worked for me in the past (I am somewhat dry air sensitive).
Having an aquarium with aeration is a better way to add water to the air. Rooms with lots of aerated tanks work really well. However, this will also just shoot water droplets into the air. Fish tanks often have other chemicals added, so things can get crusty.

 

[Nik_2213]

IMHO, you need genuine distilled water as sold for use in eg lead-acid car batteries and domestic steam-irons/cleaners...

That, by definition, leaves no non-volatile residue...

Simple domestic 'de-ionisers', meant to tame 'Hard' scaling-water often simply ion-exchange it to 'Soft', non-scaling water...

 

[Sunnysdincali]

IMHO, you need genuine distilled water as sold for use in eg lead-acid car batteries and domestic steam-irons/cleaners...

That, by definition, leaves no non-volatile residue...

Simple domestic 'de-ionisers', meant to tame 'Hard' scaling-water often simply ion-exchange it to 'Soft', non-scaling water...

Are there particular brands you use and where is the best place to obtain it? My use for it is to keep my domestic steam cleaner running as clean as it can. Thanks :)

 

[russ_watters]

@BillTre thanks, that's informative as to the overall topic, but unfortunately doesn't help me figure out what to buy at the supermarket.

@Nik_2213 where can I buy such a product? I've been using supermarket-bought "distilled water" which I had expected to actually be distilled water, but may not be.

@Sunnysdincali @gmax137 et al, I've started doing tests with various brands of supermarket "distilled" and "purified" water. I'm finding that the results, while non-zero and varied, are upwards of an order of magnitude better with the various common options vs tapwater. I'm not ready to post the results yet though.

 

[gmax137]

I'm still (see what I did there?) trying to figure out how they can label the jug "Distilled Water" if it isn't.

 

[Nik_2213]

I reckon this is down to different efficacies of distillation.
I suspect their distillation rig resembles that used for 'trad moonshine', with a near-Medieval boiling vessel / retort close-coupled to a condenser. Splash-over and spray contamination may ensue.
It may just be condensate from process steam. But, hey, it is 'distilled'...
A 'proper' distillation system has a refluxing distillation column which, incidentally, mitigates such...

If label does not quote remaining non-water content, beware...

Tangential, there's just enough variation of Methanol ='Wood Alcohol' and Ethanol ='Alcohol' boiling points due to seasonal and named-storm atmospheric pressure changes to be dangerous. Especially if 'yard-still' is operated down in valley in Winter at significantly higher pressures than uphill in Summer...

 

[Greg Bernhardt]

Microorganisms often grow in humidifiers which are equipped with tanks containing standing water. Breathing mist containing these pollutants has been implicated as causing a certain type of inflammation of the lungs.

https://www.epa.gov/indoor-air-quality-iaq/use-and-care-home-humidifiers#:~:text=Microorganisms often grow in humidifiers,of inflammation of the lungs.

“Our study showed that operating an ultrasonic humidifier with tap water resulted in particulate matter concentrations equivalent to a polluted city,”

https://www.ualberta.ca/science/news/2020/november/ultrasonic-humidifiers.html

I've struggled with this and now buy jugs of distilled water and only use it when it's really dry otherwise it gets expensive.

 

[chemisttree]

how much water does your humidifier use per day? A gallon? Why not just boil some tap water on the stove?

 

[Greg Bernhardt]

how much water does your humidifier use per day? A gallon? Why not just boil some tap water on the stove?

It's more about the minerals than pathogens since I have a filter.

 

[chemisttree]

My point was that the humidifier may be unnecessary and you could boil water on the stove instead. No pathogens or mineral aerosols.

 

[Greg Bernhardt]

Can't do that at 1am while sleeping :)

 

[Rive]

could boil water on the stove instead

Feels like an oldtimer but we just timing the laundry and skip the dryer these times.
In cold weather we would have below 20% RH otherwise

 

[russ_watters]

If label does not quote remaining non-water content, beware...

Why did I not read the labels yet? Ok, now I did:

• Brand 1 Distilled: Source listed, no quality or purification information
• Brand 2 Distilled: "By reverse osmosis and/or distillation". No quality listed, but at least I know they did something.
• Brand 2 Purified: "By reverse osmosis and/or distillation."

The numbers I'm getting are 5-35 ug/m3 for these, 130-250 for tapwater (with an air purifier running). I was thinking though that I may be finding out if the deposits on the boiler section can dissolve back into the distilled water. The particle generation spikes as the humidifier runs empty.

 

[russ_watters]

My point was that the humidifier may be unnecessary and you could boil water on the stove instead. No pathogens or mineral aerosols.

Can't do that at 1am while sleeping :)

The real solution is to get a different type of humidifier; one that's a boiler, not an ultrasonic mist generator. The trouble is, my GF likes to feel the mist on her face when sleeping. She wants the humidity really high.

 

[Greg Bernhardt]

The real solution is to get a different type of humidifier; one that's a boiler, not an ultrasonic mist generator. The trouble is, my GF likes to feel the mist on her face when sleeping. She wants the humidity really high.

I used to have one and the cleaning of the caked-on minerals was not fun. Might as well get a chisel out.

 

[russ_watters]

I used to have one and the cleaning of the caked-on minerals was not fun. Might as well get a chisel out.

Yeah, agreed. It can get nasty in there. The third type are "cool mist" that basically blow air through a wet filter, and those grow....

 

[gmax137]

When I was a young kid, we had a "vaporizer" that my mom would put into the bedroom when my brothers or I were sick. It was a glass tank with a heating element that plugged in, producing a gentle stream of steam. It had a small metal cup for the Vick's vaporub.

I was too young to pronounce "vaporizer" correctly, what I called it was the "razor bug." Ha ha that's what my family called it from then on.

I googled "vaporizer" but the current ones are all plastic looking. Adding "vintage" to the search, I found this which looks a lot like our razor bug. I remember the green glass tank.

 

[Nik_2213]

The tinted tank is supposed to suppress 'algae' ?

Tangential, I used to brew a bunch of our labs' titrants, then 'factorise' them. One of the mid-quantity range ( 5~~10 litres) had a recipe that included 5 mls of chloroform else, even stored in deeply shadowed cupboard under titration bench, the stock-tank would soon go 'hydroponic'.

What was this 'Green' eating ? The titrant's reagent, used to assay eg zinc content of creams and toe-powder...

 

[chemisttree]

Life finds a way

 

[russ_watters]

I did some "closing the loop" calculations based on the airflow of my air purifier and water flow of my humidifier. I'm getting:

• For the various "distilled" and "purified" waters, <11 mg/L of dissolved solids.
• For softened tapwater, ~63 mg/L of dissolved solids.

0-75 is generally considered "soft", but what is dissolved will be different and I don't know if the mass fraction is different for the dissolved calcium vs the ion exchanged sodium. This would suggest yes, because my unsoftened water is "hard" at 150-300 mg/L.

There's a lot of confounding factors to these tests of course and the results so far vary by as much as 100% across multiple tests with the same water. One of the biggest issues that I've mostly avoided but is still notable is that when it is colder outside my heat is on more, which both reduces the humidity(room-only humidifier) and cleans the air, by different amounts. The net result is much lower particulate at the same RH.

I have not yet noticed if the precipitate is dissolving back into the water, but I might not be cleaning it often enough to notice since the boiler section only holds a few mL of water.

 

[Nik_2213]

I'm sorry, if it was 'proper' distilled water, 'Analytical Grade / AR', there would be no residue per litre-- Within experimental error, of course, of course. And there'd still be no residue from a tonne / IBC of the stuff...

One of my less-fun experiences was discovering that the bulk AR Methanol (MeOH) for our lab had again been supplied in drums with the wrong 'lacquer' coating. This had promptly dissolved and was gumming up our equipment. I modified our biggest rotary evaporator to take a fill-line via vent-tap's side-arm, force-distilled litre after litre after litre of Methanol at 'water vacuum' pressure on simmering water bath. My anti-bumping granules stuck to the accumulating gunge, but a spoonful of glass beads just kept rolling along...

 

[russ_watters]

I'm sorry, if it was 'proper' distilled water, 'Analytical Grade / AR', there would be no residue per litre-- Within experimental error, of course, of course. And there'd still be no residue from a tonne / IBC of the stuff...

Of course. But the results are way above my ability to measure zero, so the readings at least are unequivocal at that. And the possibility of contamination by me seems small - the readings are orders of magnitude above what residual water or dissolving the scale on the humidifier should cause. So I think the likely conclusion is that the water isn't well purified and/or is somewhat mixed at the factory. Here's two samples (the temperature scale tells you the central heat never turned on). In the first it ran out of water partway through the night, and there was a noticeable spike in particulate as that happened.

 

[BillTre]

This all sounds good.

The conclusion would seem to be that your residential water supply (presuming that's your source) is not great for some reason. This leaves you with three alternatives:

1. just put up with it
2. get your own equipment and make better water
3. buy better water

----------------------------
Deciding among these requires figuring out how much good water you would need, in order to figure out the costs.
So it would be gallons of water to evaporate to raise the humidity (from x to y) in the air volume of the house (at the temperature), plus considering the turnover rate, and maybe some other stuff.
Or maybe how much water does you humidifier use when you are happy with the results.
I would personally be interested in the results if you figure them out.

Once you have an idea how much water you need you can consider prices.

----------------------------
Advanced fish hobbyists in your area would be knowledgeable about your local water chemistry and how it might be treated or where it could be bought in gallon volumes.

In labs I've been in, water came in increasing quality via:
tap (from pipes)
deionized/distilled (with or without pipes)
fancy lab equipment produced ultra-pure water.

I never heard of a lab using water softener ion-exchange purifiers.

For the home, RO systems can be bought (purity, volume, and price vary).
Some RO units also have deionizer columns.

I guess you could also just get a deionizer column and use that.
I am also guessing that these operate similarly to these water purifying devices you can put on a faucet or pour through to fill a container.