Distilled vs Reverse Osmosis for adding humidity


In the winter months, I have to run humidifiers to achieve optimal humidity levels in my digital area. By doing so we have noticed a build up of Calcium in our digital printers. In order to combat this issue, we switched to using distilled water instead of regular tap water. Now, we are still noticing the same "calcium dust" showing up in the copiers. I'm trying to figure out if Distilled or RO is the way to go. I can't seem to get a straight answer with anything I find online. Wondering if anyone has come across this issue and know if one type of water is better for the Digital printing environment. Any help is appreciated!


Active member
We currently run a RO system. We had a similar issue with a mineral build up in parts of our equipment (and on certain surfaces around the room) when running unfiltered tap water. With the RO we've not had any issues over a longer period of time than we ran on tap. I'm not 100% sure if all these numbers are correct, but when the water filtration technician was hooking it up he said our system specifically was leaving only 8 parts per million, distilled would generally around 3 ppm, and our area tap water was like 130.

D Ink Man

Well-known member
I think Gordo is on to something here. The paper stock is likely the problem for the calcium build up, not the water.



The buildup is showing up inside our digital copiers as well as a light buildup on almost everything in my room. When we run our humidifiers we typically achieve 30-35% humidity. Temperature varies from 20-24C. I didn't think about the paper being an issue. I typically air out and jog all stock before using it. Our stock is stored in the back of our shop near our large presses so maybe it is absorbing some unwanted minerals from that? Typically my stock is stored in boxes and wrapped within a package.

Bret Hesler

Well-known member
What kind of humidifier are you using? I have only seen mineral build up with misting type humidifiers and then only with tap water. The ones that use evaporation aren't typically prone to aerosolizing the minerals with the water.


Well-known member
Above reply from Bret Hesler is very accurate in regard to the humidifier.

Today's paper (and board) is calcium laden. Calcium adds opacity and brightness to the paper and is less costly than other fillers, such as clay. Calcium contamination of rollers, dampening systems and blankets is a huge problem in offset. Puzzling to me how little the topic is talked about on this forum. Digital or offset, if the paper runs through the press there will be calcium issues. It adversely affects so much and the problem is not going away anytime soon. It can be eradicated, just not by means used by the majority of shops represented on Print Planet.

Alois Senefelder

Well-known member
Hello LP and Gentlemen,

Salient Points: In general the Pressroom RH is best between 35/50%

Question 1) Do you use Pre Cut, Size Paper? 2) Are the reams individually sealed in Moisture Proof Wrappers?

Water plays a minor role in Digital Printing, the only Moisture involved is the Moisture Content of the supplied paper, which

for Digital Printing is a target of 4.5%.

Calcium Contamination only becomes a problem in Litho Printing because IT becomes SOLUBLE with Dampening --- NOT Digital.

Regards, Alois
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Well-known member
The OP said his troubles are with a digital press.

With offset, calcium carbonate is used as a filler in paper manufacture, and trace amounts of calcium carbonate can even be found in some ink formulations where it is used as an extender. Higher levels are typically present in magenta ink. In offset, calcium compounds can leach out of the paper during the offset printing process. This leaching out can be exacerbated by highly acidic or overly aggressive fountain solutions especially on uncoated papers.

How would the humidity in a digital environment be aggressive enough to leach calcium carbonate out of the paper used in a digital press? Or is there some other mechanism involved?

How does the OP know/determine that it is "calcium" dust and not some other contaminate?
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Thanks, everyone for all of the input so far!

1. I'm using an "invisible mist" style humidifier.
2. The type of stock I use varies greatly but if I had to take a stab at it I'd say it consists of 60% digital 12x18 prepackaged stock, 30% pre-cut stock from larger offset & 10% envelopes & pre-printed offset sheets.
3. The Calcium dust was confirmed after much debate from our Xerox techs/upper management. We actually had to send a sample to a lab in Toronto to test if it was our press powder or other contaminants and it came back as Calcium. So since then, I have been targeting our water as the main culprit due to the fact that I have to run these stupid humidifiers for half of the year.
4. Our large presses do use offset powder and I do believe that it is a combination of that dust with the other minerals that are giving me grief.

I'm thinking the paper thing might be something I need to look into further. Possibly storing my paper differently. If the calcium is coming directly from the paper itself...well I'm not sure what I can do with that one.


Well-known member
I too am seeing a white haze on equipment surfaces (and possibly inside them). I will make the assumption that it is Calcium. We installed a misting humidifier system over a year ago that is attached to an RO water system after having used an evaporative type system that was expensive to maintain. So, the question is, what (long term?) issues can calcium cause on equipment? I have wiped down equipment surfaces but I am a little concerned about it building up inside the equipment?



Calcium will build up and cover the various sensors within the inside machine. This causes all sorts of issues and requires a tech to come on site and fix. This means lots of downtimes and I do believe it is hard on the machines over time.

Alois Senefelder

Well-known member

I suggest: 1) Involve the Paper Manufacturer

2) Check for areas of Static round the Printer.

3) I'm finding this problem hard to believe, during the papermaking process

the Calcium Carbonate fillers are firmly bonded to the paper fibres.

4) Are you printing on "Uncoated or Coated Paper"?

5) Are you suggesting that the Humidifier Misting IS precipitating Calcium Carbonate into the atmosphere?

Regards, Alois


Well-known member
Do a search for humidification on this forum as some of these things have been talked about before. We're in Minnesota and I've used steam humidification that is controlled by the HVAC equipment. Steam humidifiers are more efficient and do not 'mist' into the air. Couple that with a GOOD R/O system and you should have a system that works wonderfully. We've been using 3 steam humidifiers by Honeywell for 8 years now. Clean them when the dummy light flashes and at the end of the season. My Techs love it here because we never have paper issues. I did everything myself but have no HVAC experience, just a little common sense.


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